You could be right with the 100 pounds or approx. 22.5k. But 40 pounds is less than 20k and I think this is a number she might see as a next milestone.
I know because we speak of a human being, weight limits and such things, but personally I think a final goal of hers if reachable or not would be to consist of 50% + out of boobs. An ultimate dream of someone with a BE fetish like hers.