How do i tell my mom i want to become a vegan/vegetarian

so i have been thinking about this for a while, but i just can't seem to get my courage up to ask her, my sister (who also wants to go vegan) has told me about the time she once asked mom to go vegan but she just denied it, how can i potentially convince her to let me go vegan?

Edit: Thank you all for the kind responses and your support.

Edit 2: thanks, i successfully convinced her to let me go vegetarian. im working towards going full vegan.