There are some good low carbohydrate recipes in our recipes section, have a browse:
https://forum.diabetes.org.uk/boards/forums/recipes.21/
The ones submitted by @Mark Parrott are particularly good 🙂
It's your Mum's birthday for goodness sake! A small slice of a cake she really likes is better than a larger piece of compromise cake, unless she really likes it too.
https://www.federationdesdiabetiques.org/diabete/recettes?field_type_de_plats_tid[]=12 if you prefer the Cuisine française. You could make a cheesecake or a tarte Tropézienne substituting the sugar with a sweetener like Stevia and making the base with almond flour and/or chestnut flour instead of using biscuits.