My Mother would agree that several weeks of PRE PT in addition to Post PT was critical. In addition to working with a therapist a few days a week post surgery... we also had various exercises that she had to regularly do 2-3 times PER DAY. That is just one place where YOU come in as the cheerleading, keeping-count (and record to share w/ the PT), Nurse Ratchet of correct form!!
We also got Mom a good recumbent stationary bike that she used a couple of times per day as soon as the PT said go. Fives years later, she pretty much keeps this up & especially if she's experiencing pain.
In addition to others' good recommendations here... applying flexible chill packs several times per day w/ leg elevation was critical to keep swelling down & comfort levels up. You can make your own chill packs in the freezer by filling freezer baggies about 1/2-2/3 full of an isopropyl alchohol and water mixture. Think it's a 50/50 blend but the nurses can tell you.
You must get her to drink lots & lots of water. Don't know how your Mom is about hydration... but my Mom hates drinking sufficient quantities of water (I think it harks back to a childhood horror of half-moon house visits:roll

.
For showering we used a trash bag with clingwrap top & bottom.
I'm glad you can be there to help her! She will need it and it will be a special time of caring / sharing for the two of you!