Jessica, I am so sorry for your loss. This is a tough road to travel. In some ways it does get easier but only because the pain deadens a bit. I am 5 1/2 years on this path and some days are good, some days are not. Sending hugs for you.
The letters are so beautiful though. They bring Jen to life on the page each time you write. And, your record of this period of your life will be true. If there wasn’t grief, it wouldn’t be your story.