Hi. My best friend, and fellow cosplayer literally has more hair than anyone I have ever met in my life. I mean that totally seriously, and I wish I could impress upon you the absolute monster hair that she has. When donating it to Locks of Love she was able to make five wigs out of her hair, by pure thickness alone, not because it was so long.
Although, recently, she has begun growing it out, and its about halfway down her back. Never-the-less, even she can get it all under a wig with a little work. Anyone can.
The trick is to lean how to pin it up, and utalize a wig cap. If I were you, I would get very good at this process. Go take a day and just practice this if you don't know how. buy a wig cap, they're like 59 cents. There are HUNDREDS of tutorials, you-tube videos and whatnot about different ways of containing hair. Do it! When you've got it down, go talk to you're mom, show her that your hair can be contained and IS contained with absolutely no damage to your hair what-so-ever.
It's really quite a simple thing, containing hair.
Is she the one buying the wig? I'm curious as to why she's wig-blocking you, it seems odd
Good luck!
Cheers!