Practice aimiing. Use her scope as often as possible, stay far back but not too far back, ie with your team but kinda in the back of them so that flankers can't pick you off. Don't be afraid to use biotic grenade aggressively instead of for heals, but at the same time make sure you're keeping yourself healed as well. Always call out who you're sleeping BEFORE you sleep them so that your team can get ready to kill them before they wake up. (and if someone just shoots at them willy nilly and wakes them up, go ahead and bitch them out). But for the most part, focus on your aim and making sure your teammates are healed.