For all of Tharja's stalking and other problematic tendencies, it's still a bit disappointing that Female Robin can't S Support her, unlike how Female Corrin can do the same with Rhajat(who may or may not be a reincarnation of Tharja) in Fates.
Of course, both Awakening and Fates have the same problem: even if you could S-Support same-sex units, you'll miss out on one or more second-generation units. Just as Male Corrin/Niles costs you Female Kana and Nina, and Female Corrin and Rhajat costs you Male Kana, this pairing would cost you Male Morgan and Noire, unless the characters were somehow able to find a workaround, so to speak.