Just my thoughts after going over this video several times and frame by frame, though it DID support my initial feelings, the clip at about 0:17, her foot up the line is problematic, even though she did put it there after the throw was made and the throw was slightly off-line, she had to reach across her body to the 1B side, technically, that left foot up the line IS obstruction. The next one was very good, the last (the dramatic Slo-Mo one) is tougher, she has to adjust due to the off-line throw but moves into the basepath. The runner begins to adjust prior to the ball re-entering the shot, close call and, depending on the sanction could go either way (i.e. NFHS fielder MUST have POSSESSION prior to being in the path of the runner rather than IN THE ACT OF FIELDING ("act of fielding" sanctions C is perfectly fine).
Nope. A fielder can camp out all day in the running path in front of the base/plate, without possession of the ball. It is not obstruction until the moment that the runner's progress is impeded. Where the runner might be in the future is not a consideration (except NCAA) At 0:17, C has possession of the ball as the runner starts her slide. I don't see any indication that the runner would have done anything different if C's foot wasn't there.
I could see an argument for obstruction on the last play, but in the moment, a competitor is gonna compete. There's no chance she is going to let that throw sail by on the possibility that it might be obstruction.
A secret about that last play...It's a favorable camera angle, and the ump actually got the call wrong. The runner was called out. My DD is 100% sure her tag missed the runner completely - LOL. It's still a cool highlight video