Hi,
Instead of "Hold with Pressure from both ends" I would tell " Hold with inside pressure in all directions "
In order to explain how to get feeling of lady in your right hand I use word "inner space" of each partner. Also this feeling in right hand should be "dynamical" - breathing and not produced statically, as if you produce it statically, you will lose it when you start to move.
Before you contact each other you should have right posture (I call it vertical part of couple, each partner has his own vertical line), both of you should produce inner space feeling in your bodies between lower back and lowest ribs which are in contact.
2nd - both of you have to produce good frame (I call it horizontal part of couple and it is shared by both partners). You have to feel which muscles are placing elbows in emphasize position to your shoulders and your wrists to your elbows. At this point you should understand that shoulder blades and shoulders belongs to back of inner space and elbows and wrists to front part.
3rd - you have to produce poise, which is turning your frame slightly to the right to match your partner (natural turn). In order to do this in right way you should both turn your right side of lower back backward trying to produce contact in your ribs .
And another important point is head. Head belongs to back of inner space, so it should work simultaneously with lower back.
So if head doesn't work properly, it could be the main thing(of course if other things are OK), that you will lose your lady in your right hand.
There are also some tips how to keep this feeling during natural movements and during revers ones. Generally as Pro-Am dancer (I am Pro), if lady has posture -poise problems I can little help to get her back to my right arm on natural movements, but never on revers ones.
But generally this topic is very complicated and this feeling should be built in dancer step by step from the basics.