At first I was mad, but...
Tumblr's full of it again. Turns out this girl's weakness is cute girls. As in; she faints around those she fancies. Which makes her unable to become the cool warrior she wants to be.
To rectify this Corrin uses a magic potion to help her overcome the weakness so she doesn't pass out on the battlefield with no intention of converting her straight.
Tumblr overreacting to **** yet again. Ignore that bait.
To view the support yourself:
http://pastebin.com/bgQC0yEa
Make your own judgement, but I honestly don't think it's gay conversion like they're making out it is.