Tamsin was the same year as Cedric and Chaser during her years at Hogwarts so of course she would know Zach. The only thing I have is that Tamsin was actually Captain of Hufflepuff her final year, the year after Cedric died.
I think her and Zach could get a long. She definitely tends to get along with boys more than she does girls! She curses a lot and tends to hackle her friends, she likes to tease but it's all in good fun. She's chasing for the Bats now and offers to be a drinking buddy!