Opinion seems divided on this. I was taught that the follower should (and would) always transfer wt immediately she is placed in the cross, and it had never occured to me that there was an alternative. My first teacher used the Basic Eight as a foundation movement, so I guess that is reasonable in that context, but doesn't this get almost hard-wired in followers' minds. I don't think I would have the skill to give the contrary signal not to change. What would it be?
It's a hoary ol' subject, but I've found that the cross being taught the way it usually is (round here) is the work of the Devil - in theory, it's all led, but in reality (usually), followers will only recognise the cross lead if it's preceded by the 8CB steps (however well led), will auto-change weight and will then be confused if you don't step with your LF, or lead a forward ocho (if they're at a higher level)... nightmare!
In honesty, I've resigned myself to only leading them the 8CB way, or not at all (except for with good followers, taught differently, out of town)... though extending the pause can be enough to stop them anticipating once there (after the auto-weight change

).
Some see it as cheating, but I'll take what I can when dancing with such (mis-taught) followers - you can take a deep breath and slightly lift your chest as you lead the cross (communicating lightness), then breathe out and sink your weight a tad to indicate the weight change invitation (or don't, if you don't want her to). Shouldn't need to, but that's not my fault....
EDIT: To clarify, she 'should' change weight in response to your step/weight change only - a normal, definite step/weight change should be all you need; and if you don't want her to weight change, but you want to yourself, then you should be able to do so without her feeling it, and thus responding. Again, in theory....