I'm a bit on the fence with this one. I do think you're being a bit oversensitive but I do also understand the sheepish feeling of having to give a "boring" answer.
Mainly, I think once they get to secondary school age and older the most important thing is to teach them how to handle these questions because they're going to be asked them forever - at the hairdressers, at work, meeting people for the first time etc.
To be fair a lot of 12 year olds would just say "nothing". But as an adult saying "nothing" would seem rude or at the very least make it clear that you have no interest in chatting.
Knowing how to give a better and more socially acceptable answer is good for the times you don't want to come across as rude/disinterested but you simply haven't done anything "exciting".
Give her ideas of how to answer. It's a social skill. Have stock answers that are probably always true or you can adapt like:
"Did you do anything exciting in half term?"
"Just a quiet one at home but it was really nice. I've got into this new tv series called X and we binged the whole thing. What about you? Have you done anything exciting recently?"
Or
I spent some time sorting my room out. I found all these old toys and donated loads. I made some extra space so now I'm trying to convince Mum to let me put a fish tank in there
"
Obviously it is adapted based on who is asking. How you respond to an optician who isn't listening is different to how you respond to Auntie Jennifer who is visiting from Canada and wants desperately to engage you in conversation.
A teenager who has the skills to (when they choose to) answer an adult fully and confidently is onto a winner. Being able to come across as confident and engage people when you want to is an exceptionally important skill. Most people learn it later. If you're able to learn to do it when you're 12 then you're going to be miles ahead of a lot of your monosyllabic peers.