So, you think
What I think has nothing to do with it.
That's what the text says.
Jesus referred to her as a dog.
Jesus called her a derogatory name and then went on to do her the biggest favour she could (and did) ask for?
Because, as He said literally right after, her faith was so great, therefore He, to use the analogy, fed her scraps from the table, and healed her daughter.
Then Jesus answered and said to her, [JESUS]“O woman, great is your faith! Let it be to you as you desire.”[/JESUS] And her daughter was healed from that very hour. - Matthew 15:28 http://www.biblegateway.com/passage/?search=Matthew15:28&version=NKJV
If anything, Jesus showed that prejudices based on race or creed didn't really fly, the parable of the good Samaritan being an obvious example.
Prejudice has nothing to do with it, as was explained by Jesus a few verses earlier:
But He answered and said, [JESUS]“I was not sent except to the lost sheep of the house of Israel.”[/JESUS] - Matthew 15:24 http://www.biblegateway.com/passage/?search=Matthew15:24&version=NKJV
Jesus was sent to the house of Israel.
The woman was a gentile, therefore He was not sent to her.
She wanted to partake of that which belonged to Israel (the miracles).
He ignored her.
The disciples asked Him to send her away.
He, still ignoring the woman, said He wasn't sent except to Israel.
She worships Him, still asking for help.
He tells her that it's not good to give miracles to those He was not sent to.
She answers, in a show of faith, that even the gentiles can gain from those miracles.
He marvels at her faith, and finally gives in, and heals her daughter.
See how that works?