I think lyra is one of the best healers in vainglory. With health items she can increase her healing. I strongly advice using this roamer build when you have someone you can skype with, since coordination is very important with this build

heroic perk-principle arcanum: whenever she does a basic attack she starts charging a stronger attack which costs mana and slows enemies. for this second stronger attack she mustn't move for a little while. with this build you try to use that slow for your team.

A ability-imperial sigil: she throws down a sigil that can heal teammates or damage enemies. when the sigil runs out of 'health' it explodes doing a burst of healing and damage as well as giving allies a speed buff. the sigil also grants vision. with this build you try to keep your team alive rather than damaging the enemy. when an ally is trying to catch up with an enemy you can use the sigil and manually explode it to give a speed buff.

B ability-bright bulwark: after a brief delay you throw an ardan-like walled zone. enemies in the zone are snared, stopping them from using dash abilities. enemies trying to get through the wall take some damagee and gain a massive decaying slow. snare does not stop speed buffs. a good example is Fortress using thruth of the tooth. he marks you giving enemies trying to get to you a speed buff, that speed buff does not get stopped, while the fortress jump does get stopped by the wall. you use this zone to protect your teammates from for example incoming enemies or to help your teammates escape.

ultimate-arcane passage: lyra teleports to the selected spot opening a portal from where you were to where you teleported to. don't overdrive this ability since it only affects the cooldown and range. the portal can be used by both teams. you can use this with bright bulwark in 2 ways:
*first bright bulwark second arcane passage: the bright bulwark snares enemies keeping them from dashing, your ultimate should be considered a 'dash' and therefor its a great escape mechanism
*first arcane passage second bright bulwark: you can teleport to the enemies and the snare stops them from using the portal to get to where you teleported from

with this build none of the heroes really are your counter since most heroes can't do enough damage to kill you when your team is near. without your team you are a very easy target.

the first item, clockwork, is very important because you're constantly gonna be healing.

second item, war treads, allows you to escape from dangerous situations. it also gets you health, increasing your healing, and the speed effect is for all your teammates near you.

third item, fountain of renewal, can heal your team while your A ability is on cooldown. also gets you some health = more healing = better roamer

fourth item, crucible, gets you lots of health as well as a great item to prevent stuns on teammates or you or blocking ults like catherine her ult.

fifth and sixth item, alternating current and frostburn, without these items you can't do any damage. you must be able to do something when your team dies, alternating current gives you extra crystal damage on every second basic attack which is the principle arcanum charge attack. frostburn slows enemies even more and has enough crystal power to really make your basic attacks stronger.

EDIT: I changed up the order of some items for a little bit more early game damage. if you run out of mana alot when using this build, maybe switch the chronograph for the void battery in the beginning

lyra can deal massive amounts of damage when she can survive the fight. stay at a distance of the enemy at all times.

heroic perk-principle arcanum: whenever she does a basic attack she starts charging a stronger attack which costs mana and slows enemies. you're getting alternating current as one of your first items. it allows you to charge this second attack very fast. in big fights I highly recommend always trying to get the second attack going.

A ability-imperial sigil: she throws down a sigil that can heal teammates or damage enemies. when the sigil runs out of 'health' it explodes doing a burst of healing and damage as well as giving allies a speed buff. the sigil also grants vision. use this to prevent enemies from getting closer by throwing it between you and your enemy or throw it at the enemy to do massive damage. manually explode it when they try to get out of the sigil.

B ability-bright bulwark: after a brief delay you throw an ardan-like walled zone. enemies in the zone are snared, stopping them from using dash abilities. enemies trying to get through the wall take some damagee and gain a massive decaying slow. snare does not stop speed buffs. a good example is Fortress using thruth of the tooth. he marks you giving enemies trying to get to you a speed buff, that speed buff does not get stopped, while the fortress jump does get stopped by the wall. you use this zone to protect yourself from assasins or enemies trying to dash towards you

ultimate-arcane passage: lyra teleports to the selected spot opening a portal from where you were to where you teleported to. don't overdrive this ability since it only affects the cooldown and range. the portal can be used by both teams. mostly use this teleport to get under the turret bevore you die, when enemies go through the portal there will be a cannon ready to shoot at them.

with this build you can do lots of burst damage, but you're very fragile. the most dangerous enemies are assasins and they should be avoided at all times. most other enemies should be much easier targets since you stay at a distance.

EDIT: bright bulwark has been nerfed quite alot lately and it isn't capable of protecting you as much anymore, so watch out

the first item, clockwork, is very important because you're constantly gonna be using your A ability to deal damage.

the second item, alternating current, grants attack speed, which allows you to attack much faster as well as the increased crystal power on your second attack which allows you to do much more damage then normal.

the third item, halcyon chargers, allows you to keep your distance as well as allowing your abilities to recharge even faster. use the boots to escape when enemies get a little to close.

the fourh item, frostburn, slows enemies stopping them from getting close to you as well as granting crystalk power which is great with alternating current.

the fifth item, shatterglass, is a very big amount of crystal power further increasing your ability to kill enemies.

the sixth item, broken myth, actually shouldn't be the sixth item, you should get broken myth as soon as as the enemy starts to buy items like kinetic shield, aegis and fountain of renewal. broken myth should be replaced with another shatterglass if none of the enemies buy any of those items

EDIT: since you don't actually use your A ability that much you could instead go for the halcyon chargers first and instead of a clockwork add an extra shatterglass as the 6th item. of course if you rather have some extra health, armor or shield, just get that instead of that extra shatterglass