If you think about where the drain is connected (to your body!!) then you need to make sure it does not get pulled out. Think if you were laying and the dress went askew and it was in an outer pocket or fell from a pocket to the ground or something. She will need to make sure the drain(s) don't get pulled. And IMO, that means keeping them near the body and protected. Putting something else in a pocket of the garment doesn't seem like an issue to me depending on where the drain is located.

And yes, I get being sensitive about sizing. But you can explain to her that it's not about her size, it's about getting something larger than her size if that's what's going to give enough clearance for her needs.

An idea for comfy house socks with treads:
https://www.gripjoy.com/collec.....r-women-x4

They also have non-fuzzy socks (i.e. flat knit), crew and low-ankle length.

I wear them and love them.

Oh my! Closest thing I can think of is DD with his post surgery bag Seconding maternity wear, and definitely loose dresses!

I'm in cancer treatment and pull out 3/4 sleeve shirts every time I go to the doctor, so that it's easy for them to access my arm for blood draws. 3/4 sleeved clothes might be helpful for follow up appointments.

Sending good vibes to you and your sister and wishing her the best. If she has to have chemotherapy infusions through a port at any point (I hope not!), there are wonderful shirts on the market that have strategic zippers (so the nurses can access your port without feeling like you are disrobing). Oncology nurses love these shirts because it allows them to keep the field where they are working more sterile. Searching on "chemo port shirts" turns up a lot of them on Amazon.