I am --or was, before the writer's block entombed me-- a professional writer, so I've written a lot of notes. A couple friends who are seeing me through this know I'm planning to ctb and have asked that I notify them if I go. My birth family knows it's likely I'll ctb, and are upset, but at least the conversations we've had have been a starting place for me to address their fears and sorrows.
Two words of caution for anyone thinking of using an email delay service to deliver the notes after you're gone:
1) Test the system you intend to use with the specific recipients. A lot of ISPs see emails from the delay services as spam, and filter them out. This varies from ISP to ISP. I've had about half my friends never receive the test emails I sent them via Time Cave.
2) The free versions of those services typically limit you to two emails per day, or 20 per month, or something like that, with one recipient per email, so if you have half a dozen emails you want to send, you might be out of luck. Or you can get the paid version, which typically allows unlimited emails (I'm a cheap bast*rd, and always use the free version).
I just posted a dedicated thread about my rather unpleasant experience with Time Cave, if anyone's interested. The short version is that those services are neither secure nor reliably private.
I would be too. Maybe you could start a "journal" that she could read later? If you start it with an up-beat, optimistic note, and keep it regularly, every other day for a month, you could get down a lot of thoughts that she might find comfort/explanation in, and it wouldn't neccessarily be recognized as a farewell note.