Get a full thyroid panel done, not just the basic TSH. Northern breeds do best on the higher end of normal range, and thyroid issues are very common. If thyroid is normal then look at Cushings.

I'd see the vet.

My dog had a weight gain that I didn't notice too much (I had just had a baby, he was getting old and slow) and it turned out to be a 10 lb tumor!

successfully removed. DEFINITELY not saying that is your case, just saying that I always err on the side of caution now.

Spayed dogs need way fewer calories than intact dogs. I would talk to your vet and ask for a body condition score, a goal weight, and a daily calorie goal. You may have to adjust the calories a bit after you start since every dog is different.

I have also found this calculator helpful.

https://petnutritionalliance.org/resources/calorie-calculator?type=dogs

Dogs can get Cushing and Addisons. I would do bloodwork.

Get her thyroid checked.

Yes, after spaying it is common that dogs hold more weight. I’d start by adjusting portion size, and maybe replacing some kibble with bulky low cal options like green beans. If a month of that doesn’t make a difference I’d go to the vet and have bloodwork done.

This is a husky/malamute mix, female 5.5 years old. I had never spayed her but she had an infected uterus last summer with emergency surgery. She always looks bulkier as winter comes and her winter coat comes back in, and she looked slim when she finished blowing out her coat earlier this year, but she's looking like a Mack truck now. It's not just the fur, she's got plenty of padding on her spine that has happened within the last couple of months. No change in her exercise or diet but is this just because of the spaying?