How Do I Convince Her She IS Taller

Olivia was perhaps the easiest child ever to potty train. We had been working with Alex for a few months and he was mostly out of diapers during the day. One morning, Olivia woke up and said "I'm wearing underpants today. No more diapers for me!" And she was right! She has been completely potty-trained during the day ever since. Sure, she did have an occasional accident, but nothing out of the ordinary. I really felt like I had nothing to do with it. She made up her mind that's what she was going to do, and so she did. (That is SO her personality.)

So now, the problem I have is that this was 6 months ago. While she has stayed perfectly potty-trained, she only rarely, very rarely, will go by herself. Usually Eric or I have to take her so that we can sit her on the toilet. She is a bit too short to get up all by herself, but we have a step stool for just that reason. She has used it on her own a handful of times, and Eric and I try to get her to use it when we take her. We tell her that she is a big girl and she can do it, but she's not buying that. She'll look at us and say "I'm not taller!" (in her 'you're so crazy!' voice).

While a part of me understands this and sees it as her need to hold on to the security of having us there with her, the other part of me is just ready to not have to stop what I'm doing (what we're all doing pretty much) to take her to bathroom 8 times a day! Does anybody have any suggestions for me at all?