If you're breaking the motor mount then you're landing too hard. You may not be face planting the plane, but that plastic mount isn't going to go to pieces unless some significant shock is applied to it.

As for your mom situation, here's a thought. She sees planes as a waste of time. You know what? She's basically right. You can't make a living with them (at least not many can), they don't give you job skills or people skills, and they cost money. Every one of us in the hobby just does it because we like it with the understanding that it takes the space of something we could probably do that's more productive. That said, you enjoy it, much like many kids do with video games or facebook time. So offer her a deal. You want time and money to pursue RC airplanes. Perhaps she wants the lawn mowed for free? Maybe she wants the dishes always washed or the laundry done? Maybe she'd like to see straight "A's" on your report cards? Offer to take on an extra chore at home in exchange for transportation and an allowance for your hobby. And, if you aren't already on the honor roll, tell her you'll work at it if you can get the plane you want for Christmas. That might mean you have to turn off the TV or the computer before you want to every night, but guess what? Us grown folks have to do that too in order to indulge in this hobby.