L.R.
Sorry to hear about the situation, which sure is stressful for all of you -- your daughter included. It sounds like she doesn't even want the items she's stealing, but maybe she does want the attention she gets from you and her dad when she steals. I'm not saying you don't already give her great attention! But sometimes younger kids don't have the skills yet to express that they want more, or different, interactions, or they're unhappy about something they haven't told you about, or their medications make them feel funny, etc. And when they lack the communications skills, sometimes they behave in ways that get them "negative attention." Though adults often wonder why a kid would do something wrong just to get negative attention, it's still a way for the kid to interact with the parent. Does she have outside activities other than school? Friends who come play, classes that interest her, sports, dance, art, etc.? Does she have hobbies and can you redirect her time to a hobby where you participate with her? That doesn't directly address the stealing, but it does give her things to be good at, and times she spends just with you.
To address the stealing: Is she getting any behavioral counseling to go along with the ADHD medications? Maybe she needs it. In the meantime, I'd go to her school counselor today (without your daughter present) and talk about the situation -- counselors often have very good ideas and have seen things you wouldn't believe; very likely the counselor has dealt with this same question before. Don't wait, though -- it sounds like you've dealt with this well so far, but still want input since it's continuing, so get professional input today. Good luck and keep on being consistent and loving.