So it was with her.

It is correct, but you don't see this very often. The "it" refers to the situation just described: not a student, but studied hard.

It's the same as writing "The same was true for her" or "The same situation applied to her." In other words, she was not a student, but she studied hard.

Thanks for your quick reply!

I understand now and I believe you, but I am still unsure of how "So it was with her." can stand alone as a sentence. Seems like I need a refresher! It just sounds awkward to me, and I am a native speaker. The alternative sentences you provided sound so much better.

Thanks again!

This structure becomes readily apparent in sentences like

The first sentence is correct and the second (sentence) is correct too.

In order to avoid repetition you can simply say

The first sentence is correct and so is the second.

Well, like I said, you don't read it that often, and you are completely right that it can't stand alone without context, but that would apply to other sentences with referents in prior sentences.

Peter went to Oxford.
Sally did too. -- This won't work unless you know what it was that Sally did.

I'm just back from a trip to Cape May. I met my husband there, you know. -- This