You may be right. I'd guess the other way, but I don't really know. Chicago Red Stars seem to have drawn about 50,000 fans to 11 games (two have no listed attendance at their website, and I didn't bother to add the other nine - I just note that the low was 3,600, the high 5,200, and if the median was about 4,500, that'd be 50,000 or so.) If you figure even 1 in 5 was a girl with dad or with mom who chose this instead of a Fire game as their once/summer pro soccer game, that's 10,000, which would be about 600 averaged across our 16 home games (or do we have 15 now?) I don't think that number is so high that it's unbeliebable. On the other hand, I don't know if the real total would be that high. I can certainly say there were teams of 7 or 8 year old girls in attendance at Fire games in previous years, and it'd be surprising to me if they DIDN'T decide to go to a Red Star game instead.
Comically, if one calls the FO and asks for the number, the very nice young woman will "go check for you," come back and say "11,000". If one then pauses to process that little gem and replies with "Even?" she will cheerfully say "mm-hmmm."
I think they were waiting to announce the attendance added with this Wednesday's game to call it a triple-header.
I just did some math and MLSnet.com is calculating the Dallas game at an attendance level of 0, so their numbers are going to be lower than mine which will be using the number listed earlier in the thread.