Yeah i could see her being DLC, beacuse most people are expecting a Geno or an Isaac as one of last newcomer reveals. (with "a" and "an", i'm referring to a high-caliber announcement that would get people talking for days)
Geno and Isaac would not work as DLC though.
Isaac is from a dead franchise. If he is included it's because of the Ballot, true, but he would be in the base game, as there would be no guarantee for casuals purchasing a character from a dead series.
Geno on the other hand is another case in which he is a third party, but belongs into the world of a first party.
Geno has been gone for many years, with 2 appearences to his name. Geno as with Isaac would not sell.
Sure they would sell and be popular amongst the hardcore Smash fans, but the casuals are often who brings in the money.
My bet is that if they will be part of the game, they will be in the base roster.