If you want to understand more about it and are willing to spend time on training, I would suggest this book: https://www.amazon.com/Mine-Practical-Guide-Resource-Guarding/dp/0970562942 It is written for dog behavioralists, but as a fellow Pyr person I have found it very helpful in understanding resource guarding in my own dog. The strategies described in the book have been very helpful to me.
Sorry you had a rough weekend. Two things that stand out from you post is that your dog is overaroused outside and has resource guarding issues.
Resource guarding is pretty common, dogs either guard from humans or other dogs or both. Dogs can guard food, toys, spaces (bed, couch etc), people and more. Since it is so common there are a lot of resources out there. Start with the book Mine! to learn about resource guarding and how train it.
As for the overarousal outside I recommend the Relaxation Protocol. It is amazing! Here is a writeup about what it is and some mp3 files that talk you through the process. Start inside your house and then slowly work you way outside (backyard or low distraction area first).
Working with a trainer is a great idea. Make sure they've worked with these issues before. There are plenty of good trainers who can teach a dog to sit or come but don't have experience with behavioral issues. How may resource guarding clients have they had? What was the outcome? Would they be ok with you contacting a previous client who had resource guarding issues as a referral? It is great that you recognize there is a problem and you're willing to work it. It is not too late to start training and helping Maya :)
This sounds like resource guarding. Here's some recommended resources on how to manage and resolve this type of behavior:
Patricia McConnell Other End of the Leash blog, Resource Guarding: Treatment and Prevention
Whole Dog Journal, Key term search Resource Guarding
Mine!: A Practical Guide to Resource Guarding by Jean Donaldson
Should the issue stay the same or worsen despite your best attempts, please do not hesitate to contact a professional, reputable, positive reinforcement trainer, or better yet, a board-certified Veterinary Behaviorist (US Directory here), you are absolutely not alone in dealing with resource guarding and this does not mean you have a bad dog.
Wow, she already is a big and strong dog at seven months and could do an incredible amount of damage if she wanted too. Your dog is resource guarding. I don’t think you should be reaching into a dogs mouth to take something from it when it is growling, baring its teeth, and snapping at you and/or your mom. That is all kinds of no. You could get seriously hurt and it doesn’t build trust with your dog. You want to completely avoid that reaction.
I would honestly recommend contacting a professional, reputable, positive reinforcement trainer, or better yet, a board-certified Veterinary Behaviorist (US Directory here). It will help immensely.
You are absolutely not alone in dealing with resource guarding. I had the same issue with my dog when he was around two to three months old. He would resource guard over high value objects like pig ears and other bones. I tried to handle it on my own and definitely got bit a few times as punishment. It sucked, and he was much smaller than your dog is right now. What really helped me is building trust with my dog, contacting a behaviorist, and reading Mine! A Practical Guide to Resource Guarding . I highly recommend that you check it out. After months of working on it, I can now reach into his mouth and grab whatever I want with zero worries and no reaction. You’ll get there, but it takes lots of time and patience.
The book is MUCH more helpful and detailed, but here is a general outline on how to deal with object resource guarding. You’ll be using desensitization and counter conditionshing. Start by making a list of all the things your dog has ever guarded from the lowest possible value to the highest.
Give your dog an item that is the lowest possible value. You want him to be able to enjoy it while you are a few feet away without any sort of reaction. You want to teach your dog that when he has this object, your presence means good things. So when he has the object, walk up close enough that he notices you (but not so close that he reacts) toss a high value treat at him that he likes a shit ton, and then walk away. You want to keep coming in a few inches closer and tossing your treat before walking away. You should eventually get to a point where he is comfortable with you standing next to him while he is chewing.
After that, you’ll want to teach him that hands around him mean good things. Start by leaning slightly lower as you toss the treat. If you see the dog react negatively at all, slow down and go back to being a few feet away from your dog. You want to eventually get to the point where you walk up to him and put a treat next to the guarded item and walk away.
When you can reach in with a treat successfully, start tossing the treat to the side. When your dog leaves the bone to get the treat, pick up the item, ask for a sit and then give the item back.
Continue with small steps. You’ll want to work on exchanging next. Let the dog hold the object for half a second before taking it back and supplying the treat. You’ll start letting the dog hold the object for longer every round before treating. Eventually you’ll start adding distance. You’ll give the dog the object, walk away, come back and take object away. You’ll increase distance until your walking twenty feet, approaching your dog, and taking away his item before treating. You should get to a point where the dog has the object for a minute before you take it away and treat. Add more time and distance and if you feel confident, it would be time for cold trails.
You’ll want to repeat all the steps I’ve mentioned with the lowest value guarded item to the highest value guarding item. If the dog guards at any point, go back and increase distance until you get a tension free exchange. If a dog is struggling at a certain step, it is very unwise to advance to the next. It is, in fact, more prudent to back off and do easier exercises and then take a stab at the problematic rung from a different angle, i.e. by juggling other variables.
I hope that helped at all. Don’t rush this. It takes time, but you’ll get there. If you see his behavior worsen, go to a behavioralist. Good luck!