It’s kind of you and your community to organize the support.
My dad had the surgery. You are right, appetite was severely impacted. Mood swings and depression are side-effects of the surgery as well. (Not associated with your question here, but since you are close to the family you might want to recommend that your friend participate in the cardiac gym facility that is offered usually at the hospital or Ann affiliated facility - a close friend recommended it to me, it really helped my dad - more than the exercise the sense of community of people having been through a chest cracked open situation - so I always recommend it now.)
Nutritionist-directed meals at the hospital were “normal” - a little bit of a lot of things, and the variety definitely helped. He could have a bite or two of a couple of things even if he wasn’t really feeling like eating.
When we got home, it got a bit harder, but we used the “well, this is how they served your meals at the hospital, right?” and managed to convince him to eat a little bit of several things too.
For the patient, I’d stick to something simple that will keep well - a very simple chicken soup with some noodles or rice on the side to be added in when eating was my dad’s favorite meal for weeks. We added some vegetables - potatoes, carrots, cauliflower, green beans, peas - to make it a complete meal even if he had just a few bites.
That said, meal trains are often more for the family at the outset I think.
So for the family, it sounds trite, but for the first meal up, a simple roast chicken or chicken parts with a couple of vegetable sides provide comfort plus flexibility with leftovers. And there is potential for chicken soup when they’re done.
Rotisserie chicken works too: when my uncle went to hospice care, we arrived home one night to a boston market drop-off including two chickens - we chuckled appreciatively because it would never have crossed our minds to do that, but it was perfect to have the simple chicken that night, sandwiches the next few days, and we did end up sticking bones into a PC for soup a few days later.
Other suggestions: Include some fresh things - fruit, a bag of salad greens, yogurt. Sweet things bite-sized and that keep well - cookies, brownies, muffins, banana bread. As an extra, quiche custard baked in muffin cups is handy for breakfast, lunch, or snacks for the patient when they don’t feel like eating a normal meal.
And if you’re very close to them, consider making a bit extra of whatever you’re cooking for yourself in subsequent days and weeks and dropping of a serving or two once in a while, to mix up their routine of casseroles, takeout, and the inevitable general rut.
Best wishes to your friend for health and good recovery, and to her family for patience and caregiving.