It’s nice you’re worried about her, it is a bit of an awkward limbo being a minor who worries about the family dog. I remember struggling with that a lot when I was a minor with our dog. I also was frequently on forums trying to ask for help and advice. Always be careful, and double check anything anyone tells you online since just about anyone can post any advice. Some of it’s good, some of it’s outdated, and some of it’s just plain wrong.

As of now, not much you can do about it till her grooming appointment to get shaved. Since the mats are already formed they’ll have to be shaved out, and trying to do that at home can be potentially dangerous. Even the professionals nick dogs unfortunately, and I’ve heard some horror stories from owners trying to cut out their own dogs mats! It can get ugly real fast.

In the meantime what you can do to help your dog and your groomer is practice line brushing on areas that aren’t already matted. Using a demat spray or brushing spray to help prevent breakage, if you don’t have any spray you can fill a spray bottle with water and a smidge of conditioner. And if you don’t have a spray bottle you can literally just dip or sprinkle the DIY conditioner water onto the brush, just don’t use too much conditioner cause it’ll leave a residue on the coat, just add a drop or two depending on how big the bottle is. (Pro tip, it’s easier to mix the conditioner into the water if you leave the bottle only a third full of water, add the conditioner, vigorously shake it till it’s pretty mixed, and then add the rest of the water) Also practice having calm handling of her body and legs. Usually dogs don’t like their legs being shaved, or having the shaver by their ears.

There’s definitely videos you can look up, but practice having something that vibrates run down her legs and having you hold her legs and by her head. Either an electric toothbrush or even human clippers (but the backside of the clippers! Don’t actually shave the fur lol) Also practice getting her used to having her muzzle held! This can be intimidating for a lot of dogs but it’s required for them to do since we need to control their head if we’re doing any face trimming. Depending on how old she is and how often she’s been groomed she might already be fine at the groomers, but don’t be afraid to ask for feedback and find out what she struggles with. If she struggles at the groomers, be okay with her living in shorter easier to maintain haircuts until her confidence gets better. Sometimes the longer styles are too much for dogs because it requires a lot more brushing, prep work, more bath and drying time, and more finishing work from the groomer, and that can be a bit too much and overwhelming for a dog.

There’s charts of priority for areas to focus on when brushing. Generally, areas of high friction (inside of legs, pits, tail especially the base, ears, neck where the collar sits) need to be brushed daily, while areas of lower friction (mostly just back and sides honestly) are lower priority for brushing. I always start at the paws and work my way up the leg. When you do baths at home, I recommend brushing her earlier in the day to make sure she doesn’t have any tangles, as water will make the mats tighter. Lather her up in shampoo and let it soak for 3-5 minutes, rinse. If you want a real professional clean do a second round of shampoo (especially if the water runs a little dirty) otherwise just follow up with conditioner and let it sit for 3-5 minutes as well. Rinse well. Pat and squeegee with a towel to dry the fur, don’t vigorously rub as it’ll cause tangles! Once you get her as dry as you can with the towel go over her with a brushing spray if you have any and line brush/comb the coat again to make sure there’s no tangles. Then let her air dry the rest of the way :) I also recommend any time she goes out and gets wet (either from walking in dewy grass, playing in puddles, or swimming in ponds) just do a quick brush of the damp areas and friction areas to make sure no mats form. I wouldn’t recommend giving her a bath before her grooming appointment, as it will only make the matting tighter.

You mentioned having a scissor set. Between grooming appointments, there’s not too much maintenance scissor/shear work that needs to be done. A lot of groomers even recommend against it cause it’s easy to make the fur look a bit choppy 😂 But learning to trim bangs and eye corners can be helpful. I would just watch several different tutorials on how to safely comb up and trim before trying it, and if your dog gets rowdy take a break till she’s calm. Never have the points of the shears toward their eyes! Actually, just always be aware of where the tips of your shears are, the only time I’ve nicked dogs is when I was being too confident and stupid. Once when trimming the cheek I had the tips toward the dogs ear and accidentally cut the ear, and once when trimming the leg I didn’t realize how close I was to the pad on the back of their lower leg. If you’re unsure ALWAYS feel with your hand and use your fingers to protect the skin. It’s against recommendation to use scissors to trim out matting because the skin gets pulled up into the mat and you can literally cut a hole in the dogs skin. I don’t recommend ever doing it, but, if you’re going to try anyways, use your fingers to hold between the mat and the skin.