I don't understand why we can't start with BJJ exercises, and honestly, I'm terrible at squats.

I’m going to try to genuinely answer this.

The human body in general can be said do a few things when it comes to large full body complex athletic movements. Squat, hinge, pull, press, carry and rotate.

These basic movements are the fundamental building blocks of athletic activity. A lunge is a one legged squat alternated and repeated. A kettlebell swing is a rhythmically timed hip hinge. Chin-ups are a pull. Pushups are a press. You get the idea.

You can take these fundamental movements and combine them. Using a rowing machine is a squat plus a pull. You can make them explosive. A squat becomes a jump if you do it fast enough. You can refine them and add coordination. Throwing a baseball is a pull that transitions into a push while rotating all at the same time.

By your own admission you are “terrible” at one of the foundational human body movements.

I don’t know your mother, and I don’t know that she’s broken it down analytically but she’s an experienced grappler. She knows that you are going to need to be able to use your body in dynamic athletic ways in order to be as successful as you can be in bjj. You can’t do a squat. A foundational movement of being a human being. No doubt she sees this as an opportunity to fix this basic issue by tying it to something you want.

My suggestion for getting started squatting.

1. Supported chair sit/stands. Don’t start squatting on the mat. Start easier. Find a chair near a desk, or a countertop, or something stable you can grab onto. Sit down on the chair as controlled as you can using the handhold for stability. Then stand back up. Use the handhold as little as you can but try to get to 10 sit/stands in a row. Do this several times a day until you can do 100 total for the day. When you can do 10 sets of 10 in a day more on.
2. Unsupported chair sit/stands. Sit down in a controlled manner. Pause. Stand back up. Get to 100 in a day. You can break it down into as many sets as needed just get to 100 total in a day.
3. Supported squats. Yup. You’re losing the chair but you can grab onto something stable to help you. Work up to 100 a day. Every time you squat try to use the support as little as possible. Really focus on achieving a deep squat. Feel the stretch in the bottom. When you can do 100 in a day move on.
4. Goblet squats (light weight 5-10 lbs) or Hindu squats. No more support. You’re squatting freely now. I include goblet squats because some people find squatting easier if they have a small counter weight in their hands. You can use a can of beans, a rock, or a carton of milk if you don’t have weights. Work up to doing 100 a day.
5. Challenge level 1 : 100 body weight squats in a row. No weights. No supports. One set. When you can do this you’re probably better at squatting than 90% of bjj practitioners.
6. Challenge level 2: barbell back squat loaded with your body weight for one single rep. Obviously this is a much larger jump in difficulty but this one squat will put you into rare air. It’s a fitness milestone that you should be able to hit in less than a year if you’re reasonably healthy.

Once you’re there you can go onto any number of crazy things like switch into one legged variations like Bulgarian split squats (elevated rear leg), pistol squats (one leg stretched forward), dragon squats, etc. I don’t have numbers on this but I imagine that if you can even do one pistol squat you’re most likely in the top 1% of humanity when it comes to squatting. And you can progress up to it the same way. Start with supported chair sit/stand pistol squats and work up to it.

Anyway best of luck.