I don’t know if it’s evident in the Russian, but this is in reference to writing for the first time, not responding to the last letter.

In Russian it can be both.

👍🏼

this is in reference to writing for the first time, not responding to the last letter.

Uly, can you give us an example? To me, долго не писала would imply she had already written them before.

For instance, if you met someone over the summer and you gave them your email address, but they never wrote, three months later, they could write "Sorry it took me so long to write - I misplaced your email address." Or if something like a death took place and someone only just got around to writing to let you know "I wanted to let you know that uncle Keith died in January. Sorry it took so long for me to write - I had to get your email address from Clair and she was out of the country."

If we were answering a previous letter, we would say "Sorry it took me so long to write BACK, GET BACK TO YOU, RESPOND"

That's not to say that someone wouldn't use this in the sense of writing back, but it wouldn't be the best choice of words.

Aha, thank you! On second thought, I think так долго не писала would imply she had already written them before OR she was supposed/expected to write, but she never did as in your explanation.