You can't tech it, actually, and the frame advantage is still there, so it's more funny than a real issue. They're still forced up and you're still at like +10.
EDIT: You can't tech it if the other guy is super heavy weight, that is. It might be possible on other weights, but it probably requires a lot harder timing.
You're right, after the stomp connects and the follow-up kick whiffs, the opponent on the ground still has to stand up right away and Rachel has advantage. But the opponent can still do a Wake-Up Kick, so it's not a 100% advantageous situation. Also, I don't think it has anything to do with weight class. I'll try it out, and if I'm wrong about that, I'll post up.
Now here's a weird thing. Record Rachel doing 9K, the stomp, and have her immediately do a 6P after that. Then playback.
Let the dummy 9K you, then start mashing 4G like usual. Rachel's stomp will connect (if you timed it right), the follow-up kick will whiff (if you mashed 4G). After that, try to do quickly do a
Middle Wake-Up Kick against Rachel.
Sometimes, your character (whose doing the Wake-Up Kick start-up) will go THROUGH Rachel, and then she'll hit you from BEHIND with the 6P you recorded (which will actually end up being her Back-Turned 4P because you're considered behind her).
I know it sounds weird, but try it out. Her going through you doesn't happen
all the time, but I think the odds of it happening are greater if Rachel's 9K hits you from
tip-range as opposed to being very close to her when the 9K hits.
Try it out.
Lastly, you can avoid this weird "going through Rachel" situation if you get up with 8G, 2G, or 6G before you input the Wake-Up Kick, because it will realign both characters. Doing it with 6G even makes the camera spin-around.