Well, there's two engineering limits that Beshine will hit that could stop further growth:
1. Implant limits. We have no idea what size those monsters are rated for, or how far they can go past said limit. But I doubt that's the limit she'll hit first.
2. Skin loadbearing limits. There is a limit to how much weight skin can support. Granted, Beshine could circumvent this somewhat by always wearing some sort of superbra and only taking it off in the water, but there is a practical limit to this. I strongly suspect that this is the limiting factor in her growth. However, as others have stated, she's blown most common wisdom on these limits so far out of the water, the pool is dry!