Kate Middleton now has her own coat of arms(left). Supposedly, Kate has the right to apply herself a crest to the College of Arms which deals with coat of arms matters. But her father wanted the whole family to be able to use the crest. That's why Michael Middleton was the one who petitioned for the coat of arms which reportedly costs 4,400 pounds. This means that
his other children, Pippa and James, and his wife Carole Middleton can also use the crest. So technically, Kate Middleton's family is the ones who has the new coat of arms.
The new coat of arms is pretty simple in design compared to the prince's. The three acorns represents the three children including Kate. The two thin white chevron symbolizes snowy mountains which represents the family's love for skiing and outdoors. The gold chevron in the middle represents the mother, Carole. It was colored gold because Carole's maiden name was Goldsmith. The Colors red and blue in the background represents the Union flag of UK and matches the recently revised Prince William's coat of arms.
For more information about Kate Middleton's coat of arms visit this link.