She looks like she is traveling with her hocks pretty close together, has a weak loin, and is just out of shape.
And while I’m all for calling the vet - good old legging up takes time…I wouldn’t start a fishing expedition just yet. But estrone & ruling out some easy things, always a good start. I’ve been told By a couple fantastic vets : “get back to me in 90 days, after 90 days of work.” Though I’ve used robaxin & Prevacoxx as needed during this phase…but she’s younger & probably has fewer miles than my old OTTB war horse. Either way, want to keep them comfortable as possible to build the hind end for that 90-day recheck. Keeping in toug with the vet, but patience, may be needed.