I hesitate to call behavior "aggression" nowadays.

Here's the most clear term for it: She's resource guarding. Most dogs resource guard to a certain degree. It's an inherent behavior that all animals possess, even humans

Simplest way to cure resource guarding is to teach the dog to "trade up":
- Give the dog a low value treat or toy. Let dog mouth it.
- Hold a high value treat in front of dog's nose.
- Dog will try to grab the high value treat. When the dog loosens its grip on the LOW value treat/toy, grab it while simultaneously feeding the high value treat.
- Repeat repeat repeat repeat.
- Eventually, add the cue "Give".
Over time and many many repetitions later, you can fade the high value treat and simply use the word "Give". But do NOT skip to this until your dog knows the behavior down pat.