If a woman who went to the mikvah forgot to the make the bracha while she was in the water, and remembers when she is getting dressed, may the bracha be made then?
She cannot make the berachah when she is already getting dressed.
In the laws of netilas yadayim, we find that a person can make a berachah while his hands are wet, and according to the Rema even after his hands have dried (158:11). Most poskim agree with this ruling, though the Taz disputes it.
The reason for this ruling is that based on the order for tevilah of a ger, the berachah for netilas yadayim is made after washing, and can be delayed even after drying (the Taz argues based on a different rationale, whereby drying the hands is part of washing).
However, there is a limit to how long the berachah can be delayed, and the Shulchan Aruch Harav (158:16) writes that the berachah can only be made immediately after drying. The logic is that the berachah can only be made while there is still a ‘connection’ with the act of washing.
In the case of the mikvah, this will apply while the woman is coming out of the mikvah, but not when she is already in the process of getting dressed.