Hi Tony. The description of your daughter's back surgery doesn't leave many excursions to participate in, unfortunately.
Roads in Cozumel, in general, are in disrepair. She is going to feel bumps, whether it be in a rented vehicle, a bus or a taxi.
I don't think Cozumel locals put much emphasis on good struts/suspension in their vehicles.
And, it also depends on how much of a "bumpy" ride she can endure.
The safest bet for her may just be the beach in Cozumel.
I cannot offer you my advice on Calica. Sorry.
Good luck. Hope your daughter gets well soon.