Personally, I wouldn't be too worried about it. My 7 year old son still doesn't know how to ride a bike either. We did try last year, be he doesn't have the balance either. With him, he just isn't an athletic child and he decided that he doesn't want to ride a bike, unless it has training wheels (my inlaws take the kids bike riding at the Huron River Metro Park in Dexter alot), so I'm not making him if he doesn't want to. I figure that if he watches the neighborhood kids riding back and forth on our block, he may change his mind.
My daughter, on the other hand, figured it out all on her own when she was 7 and she is clumsy to the point of getting injured so often, the ped wants her evaluated for PT, although I don't think it is necessary because she is very active and the most athletic out of all of my kids.
One day, after we got a "new" bike for her (a friend gave it to use because her daughter grew out of it) without training wheels, thinking that either I or her dad would take her out and teach her, but one day, she came running inside and asked us to come watch her and she did it by herself. She will be 10 in Aug.
My 15 year old son won't ride a bike at all, even though he is completely physically capable of doing so and he was in physical therapy on and off since he was 2 years old. He is just not interested and totally not athletic at all and I won't make him either, if he doesn't want to.
This is just my opinion, but if your daughter is expressing an interest on learning how to ride, then just keep with the training wheels on for a bit longer and gradually keep "shortening" them, which will make the bike "wobble" from side to side more, but will catch her before she falls and she can learn to balance that way by trying to keep the training wheels from touching the ground until you and she are comfortable enough to take them off completely.
We tried this way with my 7 year old until he decided he didn't want to do it right now.