The final battle before Nightmare Moon was banished. You want more of the back-story.... all you can get at this stage is this. There are 4 alicorns on this picture. No you don't have to look deeper into this searching for some VERY VERY small alicorns. NO. You can see only 2 of them but there are 4.
I can post the NMM vector later if you want, so you will be able to see her armor from up close.