what about a mother-daughter / women's and girls' retreat or camp? the other mothers there wouldn't necessarily be single, but they would be attending without their partners. you may be able to find something like that through an organization like girl scouts, through your church, or there are also women/girls' retreats or camps based around a specific activity, so if there is something you both wanted to learn how to do, then you could go that route. i think it's very cool that you want to do something where you can connect with other single parents and she will have kids to play with. that honestly never would have occurred to me!
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personally, i love either visiting relatives, or traveling in a way that is somewhat isolating. i absolutely love to go someplace where i don't know anyone, and i'm free to just explore - i guess i'm an introvert, because i find socializing draining, and quiet/alone time recharging. i can imagine how much fun it will be as my boys get a bit older, to do that with them and have all that time to just talk and be with them. however, if you're an extrovert and/or dd is craving interaction with other kids, then i think your idea sounds absolutely wonderful!