As I suggested, I think what you need to do is deal with Pushy Mom by guaranteeing that the girls all start out with the same number of booth slots. Then after that, the rest of the slots are up for grabs. The go-getters can then grab all the extra slots, and up the numbers for everyone if you are going to split sales evenly among booths.
At least you are not having to worry about troops coming in and poaching your slots. My son's Cub Scout pack was in one county G, in council T. Right across the road from the Wal-Mart and Kroger was another county, with council MV. When they built the shopping center, TPTB decided that Wal-Mart and Kroger were going to be too big for the little post office in my town, even though they really weren't. So even though they are physically in my town B, in my county G, covered by my son's council T, they listed in the phone book as town C, county M. So we would abide by the rules of our council and schedule a slot at Wal-Mart, only to show up and find that another pack from the other council was already there. Since there were no "rules" in council MV, because the Wal-Mart is not in council MV territory, the pack would take advantage and just show up there. Then refuse to leave. Yeah, that was always fun. Luckily it's a super Wal-Mart and they had 2 entrances and luckily we never had 2 packs show up to cover both.