Unfortunately addicts are liers peroid. They don't mean to be that way it's just a part of the lifestyle and the need to make sure they don't EVER run out of pills. The withdrawl symptoms are harsh and until you make your mind up you dont want to be like that anymore, you avoid them. Other signs are keeping her purse with her at all times, lots of energy while she is "high".
Try to get in her purse one time and watch her react like a burned cat!
I wish there was a way to help her but as was posted before until she see's the problem she will lie to herself.
You mentioned several symptoms already. You know she is doing something, her ex said so too, she lies, she steals, etc These are all tell tale signs. You could confront her but it will be up to her to change. Until she admits there is a problem, it may do no good to confront her.