Just ask your mum anytime you feel like you are ready. she will probably be more nervous and embarrassed than you.
You shouldn't be sacred cos she's been through it all and it's her job to help you. If you just can't do it write her a little letter or talk to an older cousin or friend.
But just be brave and ask...you'll be really surprised at how she reacts...expect tears cos that's her baby girl a woman now!!!
She'll be fine and she'll tell you all you need to know.