Heather is more mellowed out, I think she has her moments when she loses her temper but her normal meaner is pretty chill and bubbly. Vicki definitely gets her nerdiness and clumsy ness form heather lol
Another way to look at it is that Vicki and heather are pretty similar but Heather doesn't have the insecurity or trauma that Vicki does so her fire isn't as hot as Vicki's.