Agreed. As of right now, I don't really see anything you should be worried about.....but maybe you should post a picture of what we should be looking at...
He walks tall most of the time. Just every so often he drags himself. He eats lettuce - a variety of types, weeds outside, and fruit once or twice per week. We've been soaking him almost daily - Am I supposed to soak him that frequently?
Is this a Russian tortoise? No fruit. Lettuce should be a part of a richly varied diet, but not a staple. Daily soaks are for youngsters. Once or twice a week is plenty.
I've only seen him dragging once or twice - but it worried me. He is an active little one - loves to explore and climb things. His shell doesn't seem to bother him.
I personally find the assumption that I'm doing it wrong a very good place to start, even after 38 years. You're not doing it all wrong- but it's still a useful attitude, to find what can be improved. Examine every single aspect of care and question everything.
That said, it's puzzling. Did she have a fall at some point? The plastron looks like there may be a crack & a fold? If there was an injury, a good vet may be helpful to stabilize the site.
Coconut coir is better than mulch, but that doesn't account for this. Is cuttlebone available? UVB light or outdoor time? Humidity? If the climbing objects are contributing to the problem, remove them.