Staying heavy on the leg is key to this too. When Stew taught us this, he did it on me, and when he was heavy on my leg while he had the grips on my wrist and toes, I was not going ANYWHERE.
Another important key is getting used to droping your hips below their foot. Stew does it fast in this vid, but you have to get your hip dropped low so you can get the leg under theirs.
Once you grip up on the toes and wrist, it's basically over. If your grips are good, there is very little the person can do to resist, even if they are stronger. Stew is really big on controlling at the weakest link, for a reason.
Get Cora to rep this out 10 times each side and it will likely become her most natural escape. It's easy and effective.