"In anticipation of swelling breasts" seems like it's somewhat out of left field, but that's what it says, and given some context, might actually make sense.
Hammer-Hina believes playing with a girl's breasts causes them to grow (post #1735087), but a guy needs to do it (post #1737591). If I'm not completely mistaken, then it looks like, for this reason, she's hoping you'll fondle her boobs quite a bit now that she's all tied up. I'm okay with this.