Personally, that doesn't sound like a family for whom she'd want to babysit again. I hate that type of 'take advantage' lookout.
My DH is a SAHD and you would not believe the folks that "assume" he would just love to have another few (as many as 4

in one family) kids around the house. Especially this summer, there are a couple of regular "friends" that called -- not really asking for help but more of an "can Susie have a playdate with your daughter tomorrow" and when we ask about times, it's a long silence and then "well, I can drop her off before work and pick her up after 5 or so" -- this isn't a playdate, people, it's daycare!! The total attitutde was it would be no big deal.
We do have a couple of friends that (1) have
asked and (2) have offered compensation or we knew of a family situation and DH offered. When this happens, DH almost always says yes and tries to refuse the $$ -- most of the time it's pushed on him (and gratefully accepted).
But it's the expectation not the request that just galls me! And DH doesn't just let the kids play in the backyard or whatever -- they're always at the zoo or the pool or libarary (usually whatever is free that day because by the way, this is our choice to NOT have two incomes).
Sorry to hijack your thread, OP, but this hit a sore spot. I HATE HATE HATE this assumption that because we made the choice for SAHD that we should become the neighborhood daycare for those with two incomes!