Keleth says:
I can use Cunning Action to hide as a bonus action, but I'm guessing that's not really possible in the crowd. But if I hop behind Ilvara, flanking, I can still make a sneak attack, right?
She is engaged with other opponents, so you don't even have to flank.
The requirements for sneak attack are:
1. Advantage on your attack
or
2. You have an ally within five feet of your enemy
So long as you meet at least one of those, you get sneak attack.