I'm worried my mom might have a brain tumor..?

My mom has been complaining for about a month now of a severe headache, confusion, and loss of concentration. She's diabetic, and lately her sugar has been skyrocketing to the 400s and then plummeting to normal (about 100 something) or below normal. Also, she says her muscles, especially in her legs, have been tightening up. She has been to the doctor, but they just give her a pain killer, which also doesn't help. I'm starting to think it's a brain tumor, but I'm not entirely sure if it is... So what should I do to help?