Are the shorts created for LF or LF2?  If it is created for LF2, and your model has a curvy morph applied to her, you will need to transfer her curvy morph to the shorts.  If you are not having problems with 'Copy Morph From...', this technique will be easy to apply.  It requires selecting the shorts in the scene and using the script to transfer the morph from LF2.  

Avoid using the Fitting Room, it can get very messy, very fast.  It can help in converting clothing from one figure to another, but it can prove to be complicated and can distort the clothing to the point of being unusable.

Vary that you can use 'Copy Morphs From...', otherwise you won't be able to proceed using the app as is.  If there are problems using the feature, then you should open a support ticket.  I have seen posts of iOS version problems and I would hate to think that you are having an incompatibility issue.