Yay! Someone who gets the Trophy Wife thing LOL. =) From one girly-girl and chatty Slyhterin to another, Astoria is giddy!
As far as Theodore goes, she says that she's friendly to him as well and doesn't mind being flirted with in the past =P.
Like you I doubt that Mandy and Astoria would have known each other, but who knows what'll happen in the future. Astoria's friendly to those who a)she respects and b) are nice to her as well.
Megan, being a muggleborn is on the crap list with Astoria. Sorry! >.< But again, you never know what the future holds.