How big is she............ First thing I thought was "When did I loan you Orochi??"
Wow! They look like sisters Morgan is only 1100 grams after she laid. She just started eating for me again. I got her when she was about 800 grams and a mouser. She will take rats now and got up to about 1700 grams before she laid.
I would give her the one that is eating best, least wobble and best personality. Since it is her first snake those are important. I honestly wouldn't give a spider as her first one. What if it starts to wobble and corkscrew like crazy in a few months? That might be a bit disheartening for your sister. A normal would be my choice.