Attacking a Vulnerable target marked by Valor will put Harrier on cooldown. Quickly consuming Harrier marks will allow you to generate them faster.
Vault is powerful but must be used with caution, as enemies can attack Quinn when she strikes them. Vault can sometimes be used to cross terrain if your back is to a wall.
Use Behind Enemy Lines for traveling very long distances quickly, for farming minions around the map, or for chasing wounded targets.
After being marked, move away from Quinn so she can't take advantage of it.
Keep tabs on Quinn's position. Behind Enemy Lines can enable Valor to cross the map very quickly and attack you by surprise.
When Quinn is using Behind Enemy Lines, damaging her will end the effect.