My Mum inviting herself to everything..

I don’t have a great relationship with my mum, it’s very surface level. Since I’ve had children she’s more involved in our lives but there’s still not a better relationship between us specifically. I struggle to spend an extended amount of time with her because she does a lot of things that frustrate me & remind me of the core issues we’ve always had & why ultimately we aren’t close. She has this habit if she finds out we are doing something, days out even holidays she shamelessly invites herself. And I need to put a stop to it, I can cope with days out, but holidays absolutely not. She ruined my last holiday to the point I stayed another week to recover and actually have peace & a break. What could I say if she invites herself and I don’t want her to come? I feel like everything I say is rude & I just want to be firm but not rude, preferably prevent her from asking in the future 😂 I just don’t want to get into it, or argue.