i think that if you think you'll feel better to ask her, then ask her. personally i don't think that it will do any good, since you don't trust her to tell the truth and the fact that she'll probably not tell you if she has. i think that in time, you will know all you need to know about that and you won't have to go through the trouble and pain of asking something that you may get lied to about.
addict can't hide a relapse for long, you'll know when its time to know, i think that until you do know, you keep the focus on you and be prepared to stick to your boundaries if and when you finds out she has. keeping you and your daughter in my prayers.