It's sad when our families don't understand and/or support us.

You might try letting her know how it makes you feel when she says dismissive things to you about your illness and how helpful it would be if she could be supportive even if she doesn't understand.

If she still insists on being hurtful to you about it, then you might have to just not discuss it with her at all by politely and firmly stating that you aren't going to engage in this topic of discussion with her until she educates herself on mental health issues and can discuss it in a more informed, respectful and supportive manner.