However, what you DONT get to decide for yourself is whether or not Kara's disability will affect her at your wedding.

As someone with a disability, and with disabled friends and family members, I'd like to second this, in the kindest and most well-meaning way I can.

Specifically, I am 100% responsible for my own health, and know best precisely what I can and can't manage. I know what questions to ask if I'm unsure whether your event is within the bounds of what I can do, and I know how to contingency plan is if things go wrong. It honestly really hurts when people make assumptions about my limitations without having a discussion with me (as an example, the number of people who assume physical limitations -> learning disability is both staggering and depressing).

All that is said with the caveats that I don't know Kara, her family, or her challenges. But I'd strongly suggest not 'dropping hints' but sitting down and having an actual discussion about the logistics of the day. A:

"These are things that are happening on the day that I think you should all be aware of in light of Kara's limitations." Then spell them out one by one. "It's outdoors, will be warm without much airconditioning, there will be a lot of dust and pollen, and unfortunately there won't be a quiet place to go if Kara needs it. Medical help is also quite a way away, and I don't want to be the cause of Kara being ill. Of course I'd be delighted to have Kara there, but I also want you all to have a strong understanding of what the logistics of the day are, as I don't want to cause any undue stress or illness. If you don't think she'll be able to make it, then we'll of course have a celebratory dinner with you all later. We'll have lots of pictures taken and are happy to relive all the memories with Kara separately. Ultimately the decision on Kara's health is Kara's to make, she knows her body best, but we care about Kara and don't want to create an obligation if it's going to make Kara sick!"

Basically, I don't think subtle hints are going to work. And I don't think you are ultimately going to be able to make the decision about someone else's medical condition.

(and I do empathize, I really do ... I've had to have a this conversation with FMIL and FMIL's sister about FH's mentally handicapped cousin ... the upshot of which was a decision that he won't be attending).