I'm wondering if she is in more pain at the end of the day? You know, like how if you're not feeling well during the day, it's always way worse at night when there's nothing else to distract you? Maybe she is the same way, and would benefit from even a half-dose of the pain meds near the end of the day.
Aside from that, I found that putting babies down early for the night works a lot better than putting them down later. By early, I mean around 6pm. I know that sounds crazy, but give it a try. Babies are wired differently than older kids and adults, and they seem to need to be put down around 6pm, and will fight it less at that hour. It's good that you are putting her down awake, actually - being able to fall asleep on her own is really important for her future sleeping habits. Make sure she has eaten as much as she can possibly hold (and actually, every 5 hours is not a problem in and of itself, if that's when she's wanting to eat), and then put her down relaxed but awake at 6. Let her settle herself down. She may fuss a little bit, and that's okay. Some babies just need to kind of let off a little steam before they settle down for the night. Don't worry unless she sounds like something is wrong (hungry, wet, in pain).
As for napping, if you can establish a good bedtime, I think you're better off for naptime as well. For instance, if she sleeps 6pm-6am, then she should need a short nap around 9am, eat at 10am, and then down for a nap at noon. This one will probably last a little bit longer. For the naps, again, put her down awake and let her fall asleep on her own. It's okay if she fidgets, and sometimes it takes a while for them to fall asleep. If she wakes up crying, give her a few minutes to settle back down - sometimes babies cry and they're actually still sleeping, just restless. If you leave them alone, they'll settle back down. Just be consistent and remember that you need to direct the schedule somewhat here - don't wait for her to decide everything, just kind of keep to as much of a daily schedule as you can (within reason). Once she knows what to expect next, she will get with the program pretty quickly and it will become less of a struggle for you both.
Obviously because she has had surgery, you probably need to address the pain issue (even if she's happy, she may still hurt by the end of the day). So your schedule is bound to be a little wonky right now. Just do your best to make sure she's getting the rest she needs for now. Good luck!