Personally as a nurse I wouldnt bother with the pillow, all depends how much it would affect her sleep. We change the beds every morning and obviously change the pillow cases. That doesnt happen with brought in pillows and people are a lot sweatier in hospital (pain/infection/ridiculous heating systems) and they can get pretty gross, people never bring in spare pillowcases. If she needs more just ask, we always have loads.
Same for the water bottles. Depends if we are monitoring fluid intake or not (though most wards I've been on tend to, but that's a debate for another day). She should have a fresh jug of water replaced every few hours which let's us see how much she takes in, alternatively some people drink juice/bottled water. Just makes it a little easier for us to calculated an accurate volume and make sure shes not becoming dehydrated.
Plenty pjs/loungewear. Maybe about 3 sets, and take home when needed. She may prefer pjs even if she wears nighties at home for a bit more coverage.
Phone charger- pop a label on it with her full name.
Soap bag- body wash, deodorant (roll on better as spray can set off fire alarms), toothbrush, toothpaste, shampoo. Hospital can provide hot wipes if required but really better to have a proper wash. Flannels are great but no place to dry so would pack a few and just take home each day.
Plenty pants. Most patients dont seem to bother with Bras but I would definitely need a soft one.
Number 1 most important is any medication that she normally takes. It can take us a day or so to source rarer meds so please please please take them in with you.