This story is a sequel to High Maintenance Alicorn Fillies and You.

While Celestia was defending Canterlot from Chrysalis, one of her spells hits a mirror and splits into four, hitting her, Luna, Discord, and Queen Chrysalis. Cadence arrived on the scene, and now is the mother of four, very powerful foals.

Having no idea how to handle babysitting Changelings, or Draconequus, she leaves Shining Armor to watch over the Crystal Empire and heads to Ponyville to ask six very important ponies what to do.

I mean, a spell that got divided between four can't be permanent, can it?

Twilight cast a spell and got herself turned into a filly. Luna has tricked Celestia into believing there is no cure, and now as Luna tries to 'find a cure' Celestia has to look after Twilight the Alicorn; filly version. And heaven knows Alicorns are not born often for a reason.

Traducción Española: https://www.deviantart.com/spaniard-kiwi/art/Potras-alicornio-de-alto-mantenimiento-y-tu-990270118