<human>: Could you distill the essence of the text into 1-3 sentences?

Some backstory, my gf of 1.5yrs lives at home so she kinda needs the go ahead. We've taken trips in the past together with no problems. 

Only problem now is that her mother wanted to take her to Chicago (where we're going) a couple years ago but never got around to it, so my gf is worried that she might say no because her mom wants to take her first. (She likes getting her way but my gf would rather go with me at least this time)

Here's where I don't know what to do, I was thinking I should call her mom and say "I'm planning a surprise trip to Chicago for a weekend for her daughter, that we're staying with my friend and his girlfriend." ...something something something..  I want to make it seem like I'm asking permission but in the same breathe not...more so just like I'm having her make sure my girlfriend isn't doing anything that weekend or something. 

Should I say that? I'm open to suggestions. Or should I ask for permission instead? She's 21 and we've done this before :/ And my girlfriend really doesn't want to lie and say we're going somewhere else or she's going to a friend's house, etc.

Any input is appreciated thanks.
<bot>: how do I break the news to my gfs mom that were going on a trip to somewhere she wanted to take her