Beta Reading

Two days ago I joined a group on goodreads called Beta Readers thinking it would be interesting to help authors with their work. I still think it is. But it will be hard to find the right combination between author and reader in this group. There are just too many posts, too many offers, too many requests to check them all. Still, there were two answers to my post:

One author just wanted more reviews (no beta reading) but the second send me a story.

I had some free time today and decided to dedicate my morning to this short story, just 39 pages.

I felt like a highschool teacher correcting some homework. This wasn't reading and commenting the storyline, the characters or some illogical flaw. Practically there was no style to comment.
Alternately she startet her paragraphs with "That was when" and "And then", she put her commas at random (unfortunately I don't really know the English rules of punctuation, so I couldn't help there). the vocabulary poorer than mine. The story wasn't anything new or surprising.

All my red corrections, my blue suggestions and my green comments won't be able to save this piece of literature. "That was when" I really felt sorry: How could I sent this back with all those colorful notes without hurting her deeply? I don't want to hurt anybody. I'm always striving for harmony and I only wanted to help.

Walking on eggshells I wrote a long compassionate email and sent the text back. I don't expect to hear from her.

Does that mean I won't do any more beta reading? Definitely not. But perhaps I should stick to authors I've read.