Yes pigeon toes are when the horses's hooves turn in on eachother. Depending on the severity there are ways your ferrier can trim them to help turn them out.
My Arab is pigeon toed & it doesn't affect her at all. She walks/trots like a deer though lol.
I use her for gymkhana, barrels, poles, etc and her previous owners used her for jumping & said she had no problems. They generally learn to get around quite well.
The one thing i found with pigeon toes on my mare anyway, was when we were riding in the mountains and going down steep hills, she knicked herself and pulled a shoe once but these were really steep hills with lots of rocks & roots.
It depends on where the turning in starts. Some horses turn in right at the pastern, while others have the turning start more gradually up by the knee or through the cannon. Where the turning starts can have an effect on the horses long-term soundness and what the horse would be capable of holding up to. In addition - as others pointed out, the degree of the toeing-in can also effect soundness.
Issues like side-bone and ring bone will have to be something watched for in the future because a toed-in horse is more prone to these issues.
"Fixing" feet of an adult horse can lead to more problems than you had to start with. As long as she's not knocking her legs or tripping a lot, you should not try to fix them. Just keep them trimmed or shod based on the balance of the foot.
I wouldn't do a lot of jumping with a pigeon toed horse, but if it's mild, some light small jumps would likely be fine. I would ask your vet and farrier for their opinion though. They will know your horse and be better at assessing her capabilities.