That girl killed it, and it was all in the right arm. I've given causal lessons over the years, and people always worry over the left hand, when all the music really comes from the right. When I was about 20, I talked with a girl who could play classical like Segovia, and she told me the key is to focus on relaxation and exactness. To this day, I spend about 20 minutes almost every day playing extremely slow and purposefully and relaxed.
Funny you mention alternate picking. I play mainly blues, but also have a bluegrass background. Tony Rice is the only one I always come back to, because he broke all the rules and focused on melody instead of rules. Some players adhere to a strict down-up-down-up pattern, but Tony just does whatever makes sense. For instance, a lot of players when they are cross-picking on three strings, they will do a d-u-d-u-d-u even though it requires a lot of extra movement. If I'm doing the same pattern, I'll do d-d-d-u-d-d-u-d-d, changing the stroke only when I'm changing direction. It just sounds cleaner, at least for me. I'm not a guitar scholar, but in the Gypsy jazz world it's called the rest stroke, and this guy does a pretty good job of explaining it.
https://www.youtube.com/watch?v=odneZ_hDe3w
And speaking of Gypsy jazz, Joshco Stephan is my favorite, and amazingly I found a Yngwie Vs Django guitar lesson. It's pretty interesting.
https://www.youtube.com/watch?v=caRQv9DOy4k