The oldest and plainest word to describe this situation is "curse". You can plainly say that "Sally is a curse" and I think that most English speakers would understand.
Being a geek who like to make cultural references, both obvious and obscure, I prefer the following:
When everything someone touches breaks or becomes ruined it is called the Urkel Effect. You can say that "Sally has the Urkel Effect" or you could even say that "Sally is an Urkel".
For those unfamiliar with the character, he is from a 1990's American sitcom called "Family Matters". The character is dorky and nerdy, and though extremely intelligent, everything he is involved in that is not one of his science experiments is inevitably ruined. After destroying something and receiving evil glares from those around him he would often say "Did I do that?"
Tom Au made the next best thing that I think will mean more to more people. "Butterfingers" has long been a phrase to imply that a simple mishandling can ruin the whole thing. It likely started with sports (likely baseball) where a player could have easily caught the ball, but dropped it instead. He is said to have butterfingers. But it is that one simply mistake that could cost the team the win. In other applications, people with "butterfingers" are usually not allowed to move or lift breakable things, work on delicate projects that require a steady hand, etc.
The issue with butterfingers is that it cannot easily apply to non-physical tasks. You would likely not say that Sally as financially ruined Jack because she has butterfingers. You would say, however, that Jack doesn't have any nice things because Sally has butterfingers.