while one I can feel perfectly where she, her weight is, the second woman has me mostly guessing. Her suggestion/complaint to me was that I 'shouldn't try to move a leg that is carrying weight but only the weightless one' ..well, yes of course, but this woman is sooooo light ans soooo fast that; it's difficult for me to change weight without her anticipating/noticing and changing at the same time...even when I don't want her to and try very hard not to lead her to...also, she is changing weight on every nuance of my upper torso and so lightly that I often do not notice that she has already changed weight.
I notice that the 'feel' is as if she had only one leg extending down from the middle of her body..honestly!!
I said 'try it' and she then began to feel like an 80 lbs. bag of cement...
I hate to say it, but it sounds like she hasn't learned how to effectively do simple weight changes.
AT requires clear communication between partners. Not only do your leads have to be clear, but your partner should be clear in communicating her weight changes to you. There should be no doubt in your mind as to where her weight is.
It has been written and said that the weight change is the most basic "step" in AT, and yet it is rarely taught.
You write that you are dancing "close embrace/milonguero", but you don't say "apilado".
How much weight is your partner sharing with you? (You have to share the same amount to remain stationary.)
Many "close embrace" dancers do not share enough weight to allow their partner to feel their steps (and weight changes).
There is also a distinct possibility that she is "dampening" the feel of her weight changes with movement in her hips, knees, or torso.
This is NOT the same as being able to make yourself heavy or light. There should be a clear, definate axis from her weighted foot to her center/torso, and if you are sharing enough weight, you should be able to feel it.
If you want to find out, have her stand in front of you, "embracing" you, but without arms.
Now ask her to do repeated weight changes.
Do not change weight yourself.
Can you feel the weight change now?
Can you feel a slight shift in her torso?
Now, put all of your weight on one or the other of your feet, and ask her to have her weight on the corresponding foot ("parallel system").
Lead her to change weight by moving your torso from side to side.
Can you feel her weight change?
Do you understand where she is getting the lead to change weight?
I can't remember where this happened (I've been in "non-English speaking countries" a few ties over the past few years), but someone once told me that I spoke English very well. I thought that was an odd thing to say to a native English speaker. But, I decided that what this person was telling me was that I communicated well in English. Short, clearly understood phrases. Simple vocabulary.
AT is like that in that you, meaning both the "follower" and the "leader" are responsible to communicating clearly with your partner: weight changes, axis, momentum, etc.
I have yet to see most teachers emphasizing this to the women (although some do).
Try those exercises if you can. Maybe it is all you (but I doubt it, based on what little you've given us to work with)!