My sister 13 GS AWD tire size are: 235/45 R18. I found a set of michelin x ice on craiglist for $150 but it's 235/55 R18. Will this fit?
Thanks in advance

 

No. You need slim taller tire for winter. I'd never buy a used tire for my or family cars. It could compromise safety. Only thing to consier is brand new take off.

 

I agree for no on the used tires. Not worth the risk..you're not driving a Chevette!
I put 225/45r18 winters (Michelin x-ice 3) on mine as they were $100 less than the 235s. There are theories about the narrower tire for winter, but how often do you actually need to 'cut' through the snow?
Also you want to be working about 2 or 3% of the stock diameter.. this is the best calculator I've found that compares.
https://www.wheel-size.com/calc/

 

If you are looking to save $, get a set of 17" wheels and tires. They'll fit the '13 and should be much cheaper.