From the pics I just saw (that have now disappeared??) she does look rather lean but in a 'phew I'm glad we're well on the way out of winter' way instead of an 'oh my god' way. My older WB is looking a bit thin at the moment, rib by like yours but I'm confident he will come good quickly, just gone onto a new field too to help matters.
Re the riding thing, I'm not concerned about riding G as he's very happy in himself and certainly not struggling, he took me off for a couple of wonderful canters today...so much so I could hardly stop the beast!
Interested to see other responses though as in a similar condition situation.