I would wait until you are having bigger pains that are regular. It could be the start of labour, or it could just be those annoying pains that come with being so pregnant (like baby's head grinding on your pelvic bone, ouchy).
I am sure your mum wouldn't mind you waking her if you need support, but labour can take a while to get rolling IYKWIM so if you are comfortable waiting for as long as you can then let her sleep so she is well rested for when you *really* need her.
Good luck hun
ETA, I am sure plenty of people have told you that you will *know* when it is real labour, I always got sick of hearing it, but when I did have real labour pains, I certainly knew about it and felt a bit mean for waking DH up and keeping him up all night when I was just having nasty cramps lol
Edited by Chickoin