Sounds like you've got a little kleptomaniac on your hands. I don't think that lying/stealing is associated with ADD. But people with ADD are more likely to have other psychological problems.
I hope it's just a phase. She is 8 after all. However, I'd still consult her psychologist. This risk taking behavior could become worse, and before you know it, she could be 18 with several DUI's, shooting up haroin, and prostituting herself. Of course, that is the worst case scenario. It's probably just a phase.
Ok, the reason I asked about the meds is that this behavior by your daughter is typical of kids with ADHD. If she is off her meds, or if the meds are not working as well or running out due to time, then you could expect this behavior to worsen. Actually, your doctor should have told you about this. Which makes me think that maybe you haven't gotten all the info you need about ADHD?
There are a lot of resources for parents on how to help their kids deal with these problems. If you are interested I can give you some very good links.
I would deeply re-evaluate her situation and the one surrounding her. Especially new changes in the family dynamic. The siblings, if any, and how they are treated compared to her, if she is intentionally behaving badly due to a lack of attention, that SHE feels she needs or deserves. I'm not saying you don't pay attention to your daughter, or you wouldnt be worried. Kids act out for numerous reasons that us as adults forget about since we have aged. Put yourself in her shoes, think very hard about every aspect, and look at things in a more naive light, as she would see them. Typically kids are simple. They want love, attention, to be listened to, thought about, they want gentle guidance. They want to know and understand WHY. Often as the previous person stated, therapy and medication in the early years of development can alter a childs life. No argument it can also help, for sure. But yes, be ready to be told what you may not believe or want to hear. Most children are reacting to the ones who raise, influence, support, scold, and guide them. Does she have a hobby? This can do WONDERS for kids. Finding something they are content and happy with doing alone, can set them up for a lifetime. Kids also typically rebel the more they are given rules without legit reason, and yelled at. We forget they are growing little adults, who think they ARE adults and just need to understand in their own way. Some extra patience and attention can go a long way :) I once dated a pathological liar, and he explained to me he grew up lying, because when he told his parents the truth, they didn't believe him. Now his whole life is messed up and its almost impossible to hear what's really going on with him. Its crazy how the mind works, but what happens in childhood never fails to follow us into adulthood, continuing until someone breaks the cycle.
as a parent you shouldn't over worry yourself this stress you feel could run in with your daughters life.she may one day come to resent you if you overbear her with things and expectations of what you place on her to be normal or "the way you want her to be." Lying is a frequent thing its a survival machism to fit in from bullying to protect us from rejection and to keep our physical safety in tact if she does lie she can learn to hide her other problems that are considered flaws,.....then again you could ask exactly what is wrong with her, I mean to a doctor
question is are you prepared to accept what you hear about your daughter if she does have a problem?
and are you willing to believe its truth. Due to the fact your daughter is in early stages of development you may find its only temporary. And even if she is diagnosed with something you need to keep in mind it could be medicated at a young age could cause problems later in life and if you give her the special treatment she will never learn what it really is people expect in our modern society as what is considered to be nornmal,and the illness becomes a crutch. the best approach you can do is ask her why she is stealing I think its a very common thing for some of these younger generations. I've seen it allot and my mother works at a middle school so has she
Is she on medication ? When and where do most of the problems seem to occur?
Are you disciplining her for these behaviors? If you are concerned about her mental health, you should have her evaluated by a mental health professional.