Frankly Twilights in a better position than you anyway, all but a few of her troops are hardened veterans of the various campaigns against the other factions, she has the greatest number of spell casters in all of Equestria and the aptitude to pull of considerably powerful feats of magic, as well as numerous generals who are likely highly skilled at warfare. Given you decided to land on M&S territory and not immediately attack with overwhelming force and surprise, they are likely now prepared for you, and your armies are largely untested and unskilled due to more than a millennium of peace and tranquility under the sea, don't prepare this properly and you'll get massacred.