[Slartibartfast]

Acording to the Oxford English Dictionary (how nerdy am I, lol, me and Eugene would get on great!), there's a few definitions of the word jar as a verb and probably the most suitable for Saskia's usage would be:

"to have an unpleasant or incongruous effect"

I think she's just saying she's a little peeved and out of sorts cos she's up for eviction and with all the attitude and tension in the house.