Rated Teen because that's when we teach kids about reproductive biology. Comments have spoilers, and that's partially my bad. Sorry.
Leading Equestria for a thousand years alone required sacrifices. There are only so many hours in a day, even for the one who governs how many hours there are in a day. A choice to do one thing is a choice not to do a countless number of alternatives. A mortal pony would have to compromise. An ageless alicorn? She could simply wait.
With retirement came the chance to finally chase all those deferred dreams. And if one should prove more difficult than expected, well, there were ponies who could help with that. Plenty of mares had... difficulties with these things, and doctors helped them every day!
Why should she be any different?
I had no idea what to use for cover art. Sorry about that.