Oh..she is fun. trying on all the shells. that is actually A VERY good sign that she is healthy and normal.
Question...did you boil and cool the shells before giving them to them? Reason I ask is because someone on the hermit crab forum told me that if they dont like the "smell" of them...they wont switch, or if they switch they wont stay. . But who knows...I'm not a hermit crab expert.
Good luck wiht them, you sound like you already are a fantastic place to be , if your a hermit.
ps: popcorn is usually a big hit. Try strawberries with a tiny dab of cream cheese on them...if you havent already. I've heard a friend that I know that has several of them, say its her big ones first choice. lol.