Resource Guarding, Hackles up

[GSDMUM]

My 4 month old pup is really starting to resource guard, mostly over a favorite bone and dog food. She does not do it with me but with my elderly Shepherd, whom she loves otherwise and gets along well with. She steals his bones out of his mouth and toys but can get nasty if he is even walking by her dish. I try making her sit and stay and feed them with a large spoon ( the canned food part) and she has no problem waiting her turn with this but when it's in a bowl it's much different. Her hackles go up along the entire back. She also had her hackles up when the vet and her assistant came. She then hid behind me on the sofa and they picked her up and she was just frightened. She also pees when excited when a stranger comes in and tries to pet her. She is fine after a few minutes.

I try to have everyone, including my husband and I ignore her when we walk through the door, for a good 5 minutes until she settles down.
The resource guarding and hackles worries me. In one way she seems submissive when she pees and yet her hackles go up with strangers.

My other two shepherds were not like this at all and were very gentle and friendly with strangers and you could take a bone right out of mid chew or even food right out of their mouths and they were so gentle.
Any ideas?
I have to wait until she is spayed for puppy day care to socialize her with pups and I have been asking friends to stop by and greet her to get her used to people.