Did you ever tell her when you needed them back? I know it's polite to return things you borrowed as soon as you are done with them, but sadly many people don't and end up holding on to things until you actually talk to them and ask for it back. I've let my friends borrow lots of stuff, and very few get it back to me in a timely manner. One guy stole a bunch of CDs from me, (he claims he lost them?) another friend had some video games for years until I finally realized they were missing. Bottom line is that even though its bad on her part, it's your fault for letting her borrow them. You shouldn't just assume everyone is going to just give your stuff back. So just ask her for it back and see what she says. I don't let friends borrow stuff anymore for just that reason, I don't want to be the one who has to hamper my friends to give me back my stuff.
I'd say that you were planning to wear one or the other to an upcoming event, and ask if she's holding onto them-- try to keep it casual. Then you'd be able to bring up the other item as well, and it shouldn't seem too forced.
Asking her to give them back doesn't have to be rude-- it could just as easily be a friendly reminder. If for whatever reason she does get offended, try not to take it personally! If that is the case, I'd be willing to bet that she's like that with everyone for one reason or another, and doesn't mean it to be a personal attack.
There does not need to be a fight. Just send her a message on Facebook or if you talk to her, in person may be better. Say hey, I totally forgot I let you use my shows and skirt until I saw these Facebook pics. I have really been missing them, can you meet me somewhere and bring them please? Something like that...