There is such a disconnect to your post. YOu say "bless her heart" to your aunt, but then basically talk about how she steamrolls, doesn't act like family, causes arguements, etc. What is there to "bless" her over?
You CAN say "no" to your aunt.
But as that's not your qeustion, yes, you can say "yes" to your friends offer.
I really fail to see why your aunt has SO much power, though.