These things happen often with teachers, community volunteers, etc, that "it takes a village" mentality. Alot of times it's browny points for their kids and some parents feel it helps the teacher to be more invested, athough this one took it a bit too far.
Nah man. I never seen this. And I went to private elementary schools where everyone knew each other from church.
Teachers accepting any favors or having unprofessional relationships with a students' parents ain't ethical whatsoever if you ask me. A nice dinner invite perhaps to personally discuss their child's performance or attendance, sure...and even that's shady, and should be approved by the teachers superiors first.
But a plane ticket and a lavish ski vacation? Plus giving the teacher the child's number? Nah this is unprofessional. If I had a kid and knew their teacher vacations with another students family, and has the students phone number I'd be upset and would bring it up with faculty. Something completely unethical was going on here beyond the "making out."
If I was the principal of this school, I'd tell her ass to go be an escort and galivant around with adults all she wants. And it would've been a smart decision, because look at what can happen when teachers, students, and parents become "close." A biased grade can be the least of it.