Everyone makes mistakes. Food guarding/possessiveness is a real thing, often not even an alpha issue. It is actually a survivalist characteristic. I never blame the dogs, it has always been my own carelessness.
Pam Hamilton took on training a pretty much feral group of dogs and seeing them eat is inspiring. (video below). You can turn the food issue around. They can learn you own the food. 🙂
I'm lazier. I always fed dogs in their crates (Rottweilers, Chow, basenjis) until I got down to 2 dogs. Like tanza, they knew their spot and bowl and no stealing allowed. With treats, they learned to sit as I handed them out. My current basenji, Cara, is food aggressive with other dogs. When I give treats, she knows to go to my left and the Samoyed to the right. No treats til they are in their spots.
As for friends... some dogs are social butterflies, some limited doggie friends, some should be only dogs. You don't know how they'll gel til they have time. Give them time. Even if they don't bond, you are giving her a loving home. And even if he doesn't love her, they may both come to appreciate the company. Often dogs are unforgiving if hurt in a fight, but I personally find that more true with same sex. The breeders here may know better... trust them.
You can even do some work to change the neurological response. Usually I suggest it with cats or kids or bikes etc... but it can work here too. Crate one, or leash it to you. The moment the other comes in site, do a happy upbeat "YEAH" and toss both a treat (better if you have an accomplice so you can safely hand them one. Slowly but surely the sight of the other is "yum, treat" instead of "ready to fight". With a buddy, do the same thing several times a day in the yard, out for walks, etc. Don't bring near enough to fight... just close enough so you start rebuilding their responses. Plus, it helps to swap out who has which dog so they both get individual time with you.
As for spaying...I admit I've joined the "don't spay til you get the facts". At her age, most benefits are negligible. Plus, he knows she is intact... that may make him like her more. 🙂
When we got our first Samoyed, so many stressful things were going on, including my daughter leaving the country for 2 weeks. Pam too the dogs and worked with Cara and her dog aggression. Cujo walking amongst 15 plus basenjis, calm and confident, really made me cry happy tears. When we got Moose, he became her puppy. She adores him. She sometimes sounds like a tree-shredding machine gone wild, but she doesn't even leave wet places when she disciplines him. It can happen, just relax and let it come.