Just tell her that you are planning to do it. Be direct, give her enough notice etc, but don't beat around the bush or be wishy washy about it.
ie.
"Next month I am planning to go / do X for the weekend. I'll be gone from time a to time b. Let me know if have a conflict for that night and I'll arrange a babysitter for you...etc.
State your planned actions and take responsibility for the impact it causes.
Then do it. Go have fun.
Me 42, W 39, S8, S6, S2 M 11y, A & ILYBNILWY 11/08 Walking away from a bad situation.
