Grief is a slow process. There's not a lot you can do to hurry it along. It takes its own time. Sometimes actually trying to hurry it up will make it worse. It's important to respect your own feelings and be gentle with yourself when you're in a state of grief. Pretending it's not happening won't help. Even if the relationship you were in was no good and at one level you're glad to be out of it, there's still loss and there's still grief. You are feeling grief about your failed relationship and she probably is too. However, it is a bit unfair of her to keep emailing you just to vent her feelings or for whatever reason she does it if you find it upsetting.
Ask her nicely, as a favour, not to email you unless it's about something really important. Explain it to her that this is just holding up your healing process and upsetting you. Maybe after a year or two have gone by you can go back to being 'friends' but maybe now it's too soon as your emotions are still too raw. If she persists, add her to 'Spam'. Seriously. If it turns out she wants to get in touch with you about something that's actually important she'll phone. It's not fair for her to keep stirring up your feelings, especially if it's stuff like telling you what a great life she's having now without you. What purpose does it serve?
As to turning 40, yes, life does kind of begin at 40. (I'm 50 myself). Once you get to 40 you can't keep telling yourself that it's OK to act childishly or mess stuff up or be irresponsible all the time. You hopefully have learned a few things and are a bit more settled emotionally too. You will find that you become a bit wiser with age. Stuff that used to freak you out you will just learn to take in your stride. You might not notice it on day one, but by the end of the year you might look at your life and go, 'Hey, actually, I have started to figure a few things out!'.
"The only thing to do with good advice is to pass it on. It is never any use to oneself." - Oscar Wilde