For example, I know a sweet young coach who is almost magical in her ability to teach single jumps. Yet she (a high level skater) teaches every jump with super-crossed feet, virtually insuring that her skaters will cheat their doubles when they get to that point.
Your statements contradict each other: she teaches singles really well, but you're sure she's ruining the skaters for doubles? Unless you're actually watching every single lesson she gives and she has students working on doubles that are struggling with this, you might be making a prediction that won't come true.
Skaters should be doing singles in a more-open position than doubles and triples. Leg wraps are a no-no, but there are elite skaters who can land clean doubles and triples even with a leg wrap. It's mostly ugly and might prevent them from getting the extra rotation on the next learning progression, which is why most coaches try to stamp it out early.
I watched a double jump lesson the other day where the PSA Master-rated coach (who is awesome) had the skater land with the feet crossed purposely. It was a training drill to stop the skater from popping his double jumps by opening up in the air before landing. I don't see a need for it on singles, but she might think it prepares them for doubles or she might be having the skaters land that way so that they can use the knee up-and-out motion to check out the landing.
You could just ask her why she teaches that way.
As for the "incorrect waltz jump," there are different ways teach that jump - we just discussed that in the coaching forum. Different doesn't always mean wrong, but there should be a valid reason other than "that's how I do it."