here is your problem...

1. you let your girlfriend drive your car.

never let ANYONE drive your car.

your differential is probably fucked, maybe even your cv joints.

id get it inspected immediately.

That sucks man, tell her to pay the freak attention while driving.

On a more positive note I'm sure your LSD is fine, it's probably in your head, both tires still spin, it just transmits the torque to the wheel with the most grip, hence why you may only notice the one spinning excessively.

While driving the car pulls to the left then to the right? or do you have to jerk it back? I may be misunderstanding.

55 psi?  That excessive.  Should be at 35psi.  62 is the burst pressure for our tires.

the rim and tire they replaced may not be balanced or aligned properly.

ok i don't think it's any of the problems mentioned above.  have them check your alignment obviously, but it think what may have been done is a bent tie rod.  It's a pretty easy fix if you know what you're doing.  On my old car i had to swerve for 4 wheeler that was rolling out a driveway and hit a curb going like 10ish and i completely broke mine.  get a new tie rod possibly and have it aligned, then make sure everything is balanced.  i really doubt the differential is fucked but i wouldn't say it's an absolute no to that.  hopefully that's all the problem is.