Vicki has a small Breast Expansion kink, it's not that she fantasizes about a specific size it's just the idea of her breasts getting a bit bigger or someone pointing out how big they are or if they've gotten bigger "Jeez Vicki have they actually gotten bigger?" is a little mysteriously exciting for her.
If Someone mocks her size or criticizes her for being too big she'd snap back "Their not too big, heck they could even double in size, I'd still like em" those word might bite you Vicki since we know how big Vicki in her 30s gets lol
As for too big I think aslong as they don't seriously hinder her movement Vicki would be stubbornly proud of them insisting their not to too big. A fun too big size for Vicki would probably be maybe like beanbag size where she can rest on them comfortably while gaming but a lot of effort to stand and not expected to do chores or work.