Hi Monica,
Thanks for your question and welcome to the community. Your dog is exhibiting something called resource guarding. This can occur with different dogs around bones, food, objects, toys, locations or people.
I don't think you necessarily need to dump your trainer if you are happy with the training advice you are receiving, but you should enlist the help of a skilled positive reinforcement trainer to help you with this specialized topic. If you hire someone that doesn't know what he/she is doing or uses abusive methods such as choke chains or shock collars, you will be abusing your dog and can also cause the problems to escalate. A book that I recommend that you familarize yourself with is Mine!, by Jean Donaldson. This is the best book out there to understand and learn how to treat this problem.
However, it is not necessarily designed for the novice trainer and I don't recommend that someone buy it and then just start doing the exercises without experience. You could purchase it to help you decide whom to hire based on their knowledge of the techniques explained in the book and to give you more background and really good information about resource guarding.
Here is an example of how to treat the situation and the trainer that you hire should provide you with a scenario similar to what is listed here. If you are concerned that she will take steps towards you and bite, tether her by putting her leash over a doorknob. Otherwise, she can be off leash.
There are two different strategies that can be used at any time. One is when the dog already has the resource (the bone) and the other is when the dog is tethered so she can't gain access to the bone and the bone is out of reach. This example describes the strategy when she is chewing on the bone. I would highly recommend that she NEVER has access to objects that she guards unless you are doing specific exercises either with a skilled trainer or after you gain the confidence to do them yourself.
- She is chewing on the bone
- Stay within her comfort zone. She should be completely calm at each stage.
- Walk towards her and say, "Yes" or 'click' -- I highly recommend that you use Clickers for this
- Toss her a treat
- Back up to the starting point and move just a little bit closer next time and then Click and treat
- You can also stay at a distance and move your hand towards her (NOT anywhere close enough for her to bite you and she should be COMPLETELY calm) and then Click and treat
(This is way oversimplified -- a normal treatment plan might have 100 or more steps. This is just to give you a really rough idea of what you should look for when hiring a trainer, Okay?)
The good news is that she is very young, just growling at this point, and you are getting in there early to work on the problem. If worked on properly, this is usually not a difficult training scenario with the right training goals and trainer expertise.
The goals are to have her enjoy seeing you approach her when she has resources and to not put her into a situation where she feels like growling. This is called desensitization and counter conditioning. The trainer that you interview should speak about this as well.
I am not sure where you live, but you can look on the referral list at the school that I attended with Jean Donaldson to try and find a trainer to work with. It is called The Academy for Dog Trainers.
This can be a complex topic. Work with a skilled trainer, do not use choke chains or other abusive methods and go slow. I always tell my clients that if the sessions "feel boring" than you are probably doing it correctly. If you feel anxious, your heart is racing or your dog growls or shows anxiety, you are moving too quickly. You do not want to prove to her that she needs to bite you. You want her to get used to you being around her resources.