Wouldn't it be more like either "breasts" or "tits". Booby sounds really childish (and also has connotations of "mistake"). Also, she doesn't quite finish the word off.
"oppa...jyanakatta heidi marie san wa" is the one with booby in it. Yoshika is just having one of her breast tangents again.
Miyafuji seems like a really nice person, even if she does have a little trouble with my name.You're a Nightwitch just like Sanya?That's amazing...Booby... wait, I mean Heidi-Marie.