It depends on your integrity. how comfortable are you at lying? how comfortable are you at coaching your DD to lie? How about the 6 yr old she will be with? Can she be counted on to say 4 all evening if anyone asks? I think you would hate to have to come back and get her early. Plus once Disney has their birthdate in the computer they remember. The rules are clearly stated and you are aware of them. She is also not really that close to 4. May to Sept?
Disney counts on people's honesty, like with tickets, but if more and more people can't be trusted don't complain when you need birth certificates for everything.
Let me add I know it is frustrating because my DD wanted to go when she was younger and couldn't and she only missed the cutoff to be 4 by less than a month.