I responded to your previous request saying I thought you were doing the right thing. I say just keep her in diapers (or pull-ups if you prefer) and just don't even mention using the potty for a couple of weeks. Then casually bring it up. Say she wants to go to the zoo or wants a new toy, etc. Just say, "Oh, that's for big girls who use the potty. Do you want to use the potty?" If she says no, then don't bring it up again for another week and do the same thing again. I think eventually you'll hit upon something that she really, really wants and when you ask, she'll say, "yes" she does want to use the potty. Then put her in underwear and try it again. When you do finally get that "yes" I recommend trying this:
http://www.drphil.com/articles/article/264
It worked with my son - once HE finally decided he wanted to use the potty and be a big boy.
She probably just sees all the attention that they baby is getting and probably correlated it to diapers. Also try to play up all the things that "big girls" get to do that babies can't do and then remind her that big girls don't wear diapers.
Just remember, she won't always be in diapers and when she finally does decide to use the potty, it will probably happen very quickly.