Hi, I'm Dr. Jill. I'd be happy to address your question.
Tendon and ligament injuries don't generally heal back as strongly as before the injury, but if the injury was properly rested and Tiggy was slowly brought back into work and has had no lameness issues since rehab, it should be healed as well as it will ever be. For severe injuries, some horses can never return to their previous level of performance, but for mild injuries that are properly cared for, many horses return completely to their previous work level.
After 2 years of work, if Tiggy has not had lameness issues or swelling around the suspensory since the injury, then she's doing well. That suspensory ligament will always be more predisposed to reinjury since again, ligaments and tendons never heal back quite as good as they were originally (and how predisposed to injury depends on the severity of the original injury), but if she's currently working at the level you want her for for 2 years, the chances of issues are much lower than if you want to increase her work load or if the injury was new.
If you would like her for a higher level of work, you won't know if she can do it until you try. Definitely make any increases in work very gradual and back off at any signs of lameness.
A full pre-purchase exam by your regular vet would be the best way to fully evaluate her current soundness, though unfortunately we can never guarantee what will happen in the future. (I wish we could see into the future!)
I hope this addresses your concerns. If not or if you have any further questions, please don't hesitate to ask. I would be glad to continue the conversation.