Actually, I take what I said back.
Marlena is one of the few people that Kate truly respects because she's always given her the benefit of the doubt, even through the Sami crap. If Kate didn't care about Marlena, don't you think she'd be all over John at the moment, rather then HELPING John to mend his marriage? She knows that they are in love.
It may take a while, but we'll see their friendship again.