I can only think that maybe your family has a history of uterine or ovarian cancer, and your Mum wants you to get checked out as soon as possible to prevent it from happening? Cancer can appear at any age, from childhood to older adults, so it's better to be safe than sorry.

Maybe it isn't even cancer, you need to talk to your Mum about this anyways. It's your body, you have the right to know why she wants you to go through this. Gynecologists don't typically examine girls until they're 18 or when they become sexually active.