What tank mates is she with? I ve had a fish that held longer than she needed to b/c the other fish in the tank would attack the babies so she would keep them in her mouth to protect them. As soon as i moved her to her own tank she spit them for good and then I moved her back.
by herself? if she is not alone and there are no hiding spots she may not spit. I get mine to spit when they don't want to by the method joe jaskot posted. If not you can try stripping her...