Hello and welcome. My name is ***** ***** I have been in the dog field for 25 years. I am a Therapy Dog & AKC Evaluator/trainer/ as well as an assistance/service dog trainer, specializing in behavior. It will be my pleasure to help you today.
You mention she guards it. If she is aggressive when she has it, then it should be taken away and left out of her sight.
If it is being used for comfort then I would let her keep it. Sometimes dogs are insecure and sometimes their mothering instinct kicks in and they need something to care for.