Because your Mom was dreaming about grandchildren and a pretty cat was as
close as you could get to empathy?

Jo

My amateur psychologist take on this:  John is your long lost love,
right?  The Tortie represents John.  You found him in the dream just
like your found him in real life and it has been a beautiful pleasant
surprise.  But you also know that your parents might have ambiguous
feelings about John and especially your Dad who feels annoyed when you
travel with John.  John is coming to visit you and you have a certain
amount of anxiety about that so your parents represent that anxiety and
the fact that the cat wasn't well and needs to go to the vet is your
anxiety over the fact that your Dad has voiced a certain amount of
disapproval.

Or alternately for that last part it is your literal anxiety over John's
health which has been giving him problems for the last year or so.

And if I misremembered John's name and it is really Ed well, then...I
don't know.  :-)