i'm not sure what a lowering kit has to do with replacing a shock?
Most lowering kit manufacturers do different levels of lowering for each model, plus some come with and some without shocks.
If your missus' car is still running standard shocks on lowering springs then its not a surpise they're humped, what you will find though is that you'll end up needing to replace all four shocks to make it drive properly. Change one side and it'll handle VERY oddly, Change both rears and the back will be a lot stiffer than the front and it'll be very prone to oversteer.
Someone on here thats breaking a car should surely have a set of shocks from a sport model you can have? User "951" was breaking a 1.8TS...