Hi D,
I find it unfortunate that we can't meet to discuss this but since you're unavailable I guess correspondence will have to do. As you know my maternity leave is coming to an end, however, I regret to inform you that I will not be returning to ________. I have made the decision to stay home with Peyton. If I do decide to return to the job force it will be as a part-time employee only. I'm hoping in this case that I can provide your name as a reference?
I will provide a formal letter of resignation in the coming weeks. Like I said I would have liked the chance to discuss this in person, but I know how incredibly busy you are so I guess an e-mail and letter will have to do? Have a nice weekend out of town!