Rest, rest, rest is the best cure for her soreness. To check the area if she’ll stand up for you for a treat it would be best. If she won’t stand, the way I held my girl when I needed to was just put her side against my chest gently holding her secure and let the boyfriend handle the medicine / checking so I could focus on holding her without hurting her.
If the straw was hurting her, she would move. My girl laid on the A/C vent for 3 days after surgery, she wanted a hard/cool place to lay rather than the soft ones I offered. If she gets out of the litter box you can switch it out with carefresh just to make sure nothing gets in the incision, but I wouldn’t move her to do it right now.
To get my girl to eat I had to hand feed her, she was so sore food wasn’t interesting but if I held it to her nose she’d take it. If the medicine you have is flavored, a banana slice or some other fruit she likes has been successful for a lot of people so they don’t have to force the medicine into their buns mouth. It only took my girl about 3 days before she was moving around, eating on her own, etc. My male actually was more trouble than my girl about surgery, oddly enough. They don’t really eat pellets or hay first usually, offer up some fresh veggies she likes to try to interest her. Pellets are usually the last thing they start to eat again.
Hope she heals up fast for you. Her drinking already is a great sign. 