hmmmmm.....has your car been in an accident before that coud've damaged front left suspension?
how much lower is the front driver side than other three?
did you had the same problem when you bought the car?
although coilover is pretty expansive, but it could be your only solution to solve the height problem now.
and assuming that the springs are in good condition and installation was done right, the left front side shoudn't be too low compare to other three, theres definitely something fishy about it, perhaps you should have a bodyshop or suspension specialist check on it.