If your mum has a sweet tooth, I love the sound of Hotel Chocolat's chocolate school. There are two options available: the Bean to Bar making experience where you can make your own chocolate, and the Chocolate Tasting Adventure, which is a two-hour session of chocolate tasting and how to pair it, with prosecco thrown in for good measure.
FYI, you can either book this for this weekend, or buy it as a gift card so your mum can pick her own date to go. Also, if for some reason you're on this post and not based in London, they also have non-London locations.
Price: £65 for the Bean to Bar making experience, and £50 for the tasting experience
Book chocolate making here and tasting here