According to reports, since DC has done the reboot with the New 52 (which will be going through another change soon), they effectively rewrote a vast majority of characters, while dropping others. In the original DC Earth, they pretty much killed off all the New Gods, like Big Barda (who was a former Female Fury). In this version for the movie, they said Steppenwolf is based on the New 52 version who is Darkseid's uncle. In the movie, Steppenwolf leads a massive army to earth, which they said is based on the "Knightmare" Batman had with all the Parademons, etc.
After the steady drop in ratings and budgetary problems, I'm surprised they even renewed Supergirl. Didn't they establish that the Supergirl world is in another different Earth? In the Supergirl episode where The Flash appears, they state that he is from an alternate universe brought there by the power boost from the tachyon device. If they brought Supergirl into the Flash/Arrow/Legends of Tomorrow universe it would effectively "jump the shark". Though, seriously hoping they bring in Kevin Smith to write/direct on Arrow, then things might turn around.
And, not surprised, Marvel's Most Wanted is once again DOA at ABC.