SBFAMILY I did not see that game but I know who you are talking about. She did pitch against us. I didn't see it so I can't comment on it.
I do think that it is tough for the umpire to call in real time. The base umpire is normally off to one side or the other of the mound and can not get a good look. The home plate umpire is concentrating on watching the pitch location and if they spend too much time watching the pitchers feet they will get fooled. However, it is often very clear where the pitcher is landing when she is outside the pitching rubber because often this area of the diamond is clean and level. After a few innings when there is a 2 - 4 inch rut dug in there and it is 8 inches or more outside the rubber well that to me seems obvious.
Having said that I think it is an advantage at this point for a pitcher if she can do it effectively because it is not an angle that the batter sees very often. If I were to coach agaisnst a team that I knw had a pitcher who did that I would at the very least plant the seed prior to the game and then let the umpires deal with it as they see fit. Theres not really much more you can do. Once the game is on I don't see the umpires being influenced by it being brought to their attention because then it makes it look as if they have been missing it the whole game, and nobody likes to have that pointed out.