I DON'T have experience with this - my guy was a late crawler (11mos) and walker just one month later (12m12days).
BUT I don't think I'd worry too much about it if I were you - particularly since she's demonstrated that she CAN walk. She's just choosing not to at the time. When she has a big enough reason to she'll get up and go - and then you'll have to sweep your own floor - no more dusty baby knees
Does she wince, cry or otherwise indicate that she's in pain when she stands/walks? I ask because two weeks ago my 3 year old refused to walk and only crawled - he had some issues that were worked out through visits to a chiropractor and a physio therapist but all is good now.