Look at the PDF carefully before sharing it. Most academic publishers put a timestamp on it that reveals who downloaded it, at least at institution level. Sometimes this is even embedded as metadata. If the PDF says anywhere “author personal copy”, please don’t share it on the author’s behalf.

This is mostly to avoid getting them into trouble.

Otherwise, go and share, authors love it!

Considering the version you were given by the author could be watermarked in some way, and they could get into shit from a publisher if you uploaded it for mass retrieval, you ought not to do this without their express permission. It's different if you had downloaded the article from a journal/database yourself, or if it was some other version (like an unformatted manuscript).

I've never done it, but I though there was a way to upload docs to Z-lib

Research Gate exists for authors, though I don't think it would let you post others' work.

Check academia.edu

I have never used it, but seems like my uni is uploading there. Im getting emails when someone is reading my article

Is there an option to add to Z-lib?

You might want to get her permission before sharing it. She might be okay sharing it individually, but not publically.

Have you checked the author doesn't have it linked on her researchgate or lab website? As in, it might already be available, just not easily searchable.

You can try contacting annas-archive.org