How can I convence my mom to let me get a ferrit ?

How can I convence my mom to let me get a ferrit ?

Well, I think that completely depends on her stance on it. That sounds like something that you need to have a detailed discussion about what her objections are, and address each concern. Ferrets aren't legal to keep as pets everywhere, so if you live in an area where they aren't then you likely won't be able to convince her.

If they are legal where you are and she is worried about your taking responsibility for a pet, maybe you can work out things to prove your responsibility for example by taking on a new regular chore that you can earn money towards taking care of a pet, and collect information about how much it will cost to take care of a ferret and how you will be able to afford that, and keep up with the new chore for several months showing her that you're serious about making it happen.

If she is worried about ferrets in particular, maybe you can collect documentation about them from various sources online that describe what about them makes good pets.

In order to have a chance of getting your mother on your side on this issue you'll have to have calm, logical discussions about it and not let yourself get frustrated or insistant or else she's like to just stop listening to your argument.

I hope this helps!