Eyrie of the Stars said:

LB placement is 75% the mare's strength and only 25% their offspring's strength, so the higher girl is probably a bit stronger herself. Also I took a look at her and she's only produced 1 EEE with a bunch of W and WW combo foals, whereas half of Caletta's production is EEEs, so that probably evens things out in the production side of things.

Because placement is so heavily weighted to their own strength, Caletta probably isn't going to go higher even if she churns out WWWs from here on out, because there will be new girls debuting and whatever buff she gets from more strong offspring will probably only be enough to offset them. There is a chance that RF could be super friendly and she produces a foal that's much stronger than herself, but I wouldn't bank on that. The only thing you can do is keep matching her well and see what happens.

This doesn't mean she's less valuable than your other girl though. If she continues to throw WWWs, especially if they land in the top 50 LB, then I'd consider her worth more than your other girl who might be higher but isn't leaving any legacy. So if you want to get her art and can reasonably afford tier 1, I'd say go for it!