I thought that she may have had to take steroids post surgery (quite likely)
Or perhaps as she was due to have unavoidable downtime after a big operation she might have also had a cosmetic procedure a few weeks after the abdominal surgery (less likely)
She is one of the most photographed women in the world and if she wanted a procedure on her face now would be the perfect time to get it. She is slim, outdoorsy and some people say a smoker so may have wanted a little work while out of the public glare. I don't mean a full facelift as she is relatively young for that but maybe a blepharoplasty or a brow lift?
Im sure any significant abdominal surgery could leave a person feeling super vulnerable, particularly if bowel related. My other half had stoma surgery last year and it took months for him to gain any kind of confidence back. We had a family wedding 4 weeks after the surgery that he was desperate to attend and it really set his recovery back as he was exhausted for weeks afterwards.
The car photo today makes it clear she doesn't want to be photographed at all so I am surprised she was traveling in the same car as William.