your girl is fine - you've checked everything you can so as an owner of a cav you would be just what I would look for in a breeder
it would be a real shame for this breed to die out - they are the friendliest dogs I've ever come across - its dogs like yours that will hopefully help the breed to survive
I have a 2.5 yr old cav who has very mild Sm - so can see it from both sides -I wouldn't be without her and as it's mild luckily it doesn't cause her any pain - she's just a bit "odd" at times