It's not uncommon for dogs to guard desirable resting spaces, especially if they have a history of being disturbed when they're relaxing (this is especially common for little dogs, who are often over-handled, as well as dogs who live with children, and older dogs or dogs that have health issues that may make them uncomfortable). There are three strategies we'll be using to deal with this:

Targeting: Teaching a dog to touch a hand target is a fun and easy to teach behavior that will help you "steer" your dog when needed without putting physical pressure on her.

Stationing: Being able to ask your do to go to a bed or mat is a great way to give her an alternative for being somewhere that may cause guarding. This is especially useful if the dog tends to guard your furniture, and you'd like to use it, as well!

Counterconditioning: Counterconditioning is the process by which we teach a dog that the thing that normally triggers them (ie someone approaching their space) is actually a predictor of good things (ie delicious food). You can do this by creating training setup whereby the dog is in their highly coveted resting space as someone walks past. Each time the person walks by, the dog gets food. You can either do this with one person walking past and another tossing the treats, or you can be both the passerby and the treat-tosser, depending on the situation.

Note: If you have any concerns that this behavior could result in injury to yourself or another member of your household, it's important to reach out to me or another force-free trainer in your area that can help you create a plan specific to your dog's situation. This is especially important if there are children in the home.