Remember that she this is the age when most kids lose weight anyway...combined with the fact that their eating habits change, they are moving around much more and they start to shed their baby fat. So, don't worry about her losing weight, I'm sure it's just normal.
You can also make popsicles that are just juice so she's not getting any of that extra sugar or preservatives that might be in storebought pops. You can buy cheapo molds at WalMart and Target. Also, Motts makes some that look like Flavor Ice, I bought them at Costco recently.
Kids go through phases where they only want to eat one thing all the time and She may be off her faves right now, but she'll find new faves and may or may not go back to the old ones.
Just keep offering her healthy food and she'll eat when she wants. Hang in there! it is tough to see them not eat, but it's worse to pressure her and make a big deal out of it, especially because if you make a big deal about it, it could turn into a power struggle game for her to play.