She was still a Republican back then, and voted for him in the Penn. Republican primary. Maybe it was partly an anti-Bush vote; I don't know. But, well, if you read that New Yorker article, there is no way you can come away from it not being a real friendship between Kerry & McCain.
http://www.newyorker.com/archive/1996/10/21/1996_10_21_130_TNY_CARDS_000377420?currentPage=1There must have been SOMETHING redeeming in McCain's character for them to be friends for a good decade or so. And I don't think it was just McCain's naval service: lots of vets have crossed Kerry's path before including fellow members on the POW/MIA committee, and he wasn't good friends with them the way he was with McCain.
To a certain extent I come at this from a different angle: I was not always a Democrat, but an Independent, and I liked McCain. I liked a lot of what he said in 2000, and I was impressed with his work on the POW/MIA committee -- McCain is the reason why I even learned about Kerry in 1991. He was the tall, quiet guy standing behind John McCain on C-SPAN (I watched them arrive back home from Vietnam). It is more difficult for me to separate the two, since that was how I was introduced to Kerry.
To a certain extent this is all quite painful, and it's easier to simplify and say McCain was a total snake and Kerry was only arms length "friends" with him (as in, "my esteemed colleague from Arizona"), but I honestly don't think that is the truth. I have friends who don't always live up to my values, but I find I can be friends with them focusing what I have in common with them. Perhaps, that is how the Kerry/McCain friendship worked for over 10 years. I also think that McCain has showed temper and anger when Kerry's name has come up; another indication, that this was a real friendship that is no more, because of McCain's actions.