Having babies doesn't stop a horse from being ridden for 3 years....there is more to this than full honesty and upfront is telling of.
A vet and farrier look-see would be mandatory since already disclosed she has side-bone....often what is disclosed may not be the entire scenario and I will say maybe it has progressed and the owner is also not in the know of how much progression.
Are you looking at taking on a animal with limited time of sound riding and comfortable without medical intervention of drig and treatments being faced.. Ultimately, it is going to cost plenty or some rough decisions to face.
If you are open to spending thousands for a animal that may only have a year or so to enjoy astride...
GO see the animal in person.
Be very critical of what is in front of you in build and be super critical cause it is the build that is creating the issues.
The fact the horse was off for 3 years waves a red flag, she was made to carry 2x also added issue to her ailment...
You need a vet, a farrier to share with you their knowledge and for you to do some serious research from reliable resources...
I would be hesitant though and the fact the owner already said she will take less "to a good home" is waving that red-flag at me a bit more...
Go look, handle and ride... be vicious in your eval.
If you like her that much, get the vet out and one who is well versed in lameness issues and then, your farrier to come and see if he can work with, make less the issue cause it never goes away and is there room to make changes to keep the animal comfortable and ridden since no-way would I spend $ for a pasture pet, by me they are to abundant and needing homes.
Be prepared to walk away...you do not want to take on someone else's financial problems or a horse who faces some difficult decisions in to short a time in your ownership.
🐴.... jmo...