My 2.5 yr old is doing exactly the same thing! She was fully tt up until about 2wks ago, when she decided she isn't doing it anymore.
The only thing that was different, was the night before she decided she wasn't going to the toilet anymore, was she wore knickers to bed, as she had been dry at night for about 2 weeks.
I'm guessing most kids must take a step backwards, as my son did the same sort of thing when he was tt.
Only thing I can suggest is that if she is willing to sit on the toilet/potty, is to encourage her to sit every 30mins to 1hr. Give heaps of praise when she does go and ignore any accidents!
Good luck....hope things change for you again soon.