Hi, I commend the previous owner for telling you all of that. It shows that they truly care. If it were me I would have her right hock x-rayed. Two to three films should be enough. Cost is usually $35-50/ film. If there is arthritis in that one and she is stiff in both then more than likely she has arthritis in the left too, but save yourself the $ and do only 1. I recommend going to an Equine Hospital or University for this. They usually have better equipment and experience than most mobile vets unless you live in a heavy horse area. See what the vet sees and then if they see any arthritis I would personally inject her. I have cutters down to pasture horses and have had hock issues in a 3 year old that was in cutting training and came up lame and recently a 15 year old Paint gelding that has had a very easy life and spent most of his life well cared for in a pasture. With that said, hock injections are great for them, especially if they are being used. There are no side affects and make the horse so much more comfortable. Just make sure that you are monitoring her hocks via x-rays each year. You just want to make sure that there are no significant changes over time that might cause permanent damage if she is used too hard. Also make sure her feet are trimmed properly (properly is the key word here) every 5-6 weeks. This will prevent many, many issues and keep her hocks healthier. Have fun with her and she is lucky to have someone who cares enough to look into keeping her feeling good.