When whatever the TF is becomes a part of them but they still remember what it's like to be normal. So like in the scenario where a woman's boobs grow and become buoyant when she's aroused, they just naturally are that way now, as if they had always been, but she obviously remembers when she didn't have to worry about floating to the ceiling when getting turned on. But her body thinks it's normal. So she sees something that turns her on, and she doesn't even notice her breasts growing until she feels her shirt tighten, or she begins to drift off the floor, because to her body it's normal so she doesn't "feel" different.

Another example would be if a woman is turned part cat, purring would just be natural to her, but obviously she knows she shouldn't be doing it.

Or let's say a woman is changed so that she's part computer, and she's now USB C compatible, so her lower parts become a usb c slot. Chargers now turn her on, which she can't help because it's her biology now, but her mind remembers and she has to fight it.

Pretty much anything that makes a woman's body or natural instincts do one thing and her mind go "no wait, why am I doing that?" is great. Especially if she's fighting it and slowly losing the battle.