This is a tricky one, as the older generation still have the caste rules and apply them to marriage.
You are right that there is no jaat paat in Sikhi. You seem to be okay from your family's side that they support your view of not supporting caste. However your female friend is not, as her family have already given her a set of rules to abide by. It seems like they've said she can choose her own marriage partner, but as long as he is of so and so castes. This is quite silly, as then they are not following Sikhi, but applying their own rules.
From what you have described about yourself and your family, sounds like they will not have to worry about their daughter being married off to somebody that is only marrying her for materialistic reasons. So that's one positive point. The next point is how much faith they have in their daughter that she hasn't chosen a wrong guy. It all depends on the relationship she has with her parents that they will be willing to give their blessings. Although she has does everything as correctly as she can, chosen somebody that believes in Sri Guru Granth Sahib ji (I'm assuming you do follow them and go to a Gurdwara which has Sri Guru Granth Sahib ji in it?) and not let caste be an issue, the problem lies in their set of rules that they laid out to her.
The thing is nobody can tell you what the best way to convince them is in case it backfires and makes them angry. Are there any elders that know both sides of the family, that could talk to them? Sorry, that's the only thing I can think of that will help develop trust in you. Trust is what needs to be present within both families to accept each other.
planning to buy it as she is on heavy duty steroids as NSAID can't be used , they have caused bone density problems last time she ended up with two broken thumbs and a broken arm . I had to take her down for a hip xray , Waheguru Kirpa karan she doesn't have a fracture .. If I can get her off the Tramodol and start healing her arthritis then there I would be happy.
A colleague used it and had good results so I thought I'd give it a go.