Hello, I'm Dr. Deb and will do my best to help you today.
I'm sorry for this concern for your dog.
As your vet probably mentioned to you, a heat cycle lasting this long is not the norm so I'm glad that you're having her spayed. My concern would be that she has cystic ovaries which are constantly producing hormones. If your plan was not to breed her, then having her spayed is the best thing, health-wise, for her.
Many patients will excessively lick their incisions although, of course, not all of them do. But for those patients who can't leave well enough alone, then often they will need to wear a cone to prevent access to the area. These can either be purchased at local pet stores or your vet should have them.
In terms of how long it will take for her incision to heal, there may be some variability about that, especially if her ovaries are producing estrogen. The average dog will have stitches removed in about 10 days although some vets will bury the skin sutures which will dissolve over time. But the incision itself should be healed by 7-10 days. However, having said that, if she has more estrogen in her body than the average female who undergoes this procedure, it may take her just a few days longer to completely heal.
I hope this helps. Deb
Thanks for the rating; it's greatly appreciated.
Best of luck with Milly. Kind regards, Deb