Have you tried educating her a little more? Maybe show her some literature or go online with her to assure her of their relatively small size and docile nature.
As stated above hiding things from your parents is not a good idea. You don't want to lose her trust, not when you'll be moving out soon leaving only more reasons to worry about you. Try to teach if not try to wait, the snakes, as cool as they are are not worth lying to your mother.

Hope you man up and make the right choice brother.