Question

I knew her for nearly four years. is it correct?

Answer 1

The given sentence should be written as shown below:

I have known her for nearly four years.

or

I had known her for nearly four years.

We don't use 'For' referring to time in Simple Past Tense. Present Perfect Tense with 'for' or 'since'is used to refer to the length of time an action has lasted.