Susan's investigation into this hypothesis may not be complete, but I'd think "baby's first XP bottle" is pretty telling evidence.
I'm not sure Susan should have to make an effort to hold anything up given the presumably elastic waistband, but I've been losing weight recently, and I have some older pants of my own that are perfectly fine until I try walking in them, so... Maybe? I'm not sure. I liked the idea of her arms being like that while deducing, so here we are.