Short answer: No.
Longer answer: Definitely not.
(This isn’t spoiler marked because it’s such random fan speculation, but you can assume that minor spoilers start here.)
The fan theory that Sera is the Goddess of the Hunt, Andruil is based on a few things:
- Sera claims to have an innate ability to fire a bow.
- Sera is antagonistic with Solas.
- At one point, Solas remarks that Sera is “no longer elven.”
- Sera has a deep fear of the Void, where the forgotten ones (elven gods) were sealed.
- Sera enjoys killing dragons.
For each of these, there are very easy counterpoints:
- Sera is lying about having the innate ability to fire a bow. She just doesn’t want to share her past. She’ll admit as much if you become friends with her. Even if not, lots of people can fire a bow.
- Sera has more than enough reason to be antagonistic with Solas. She’s ashamed/angry about her elven heritage and he’s all about elves.
- Solas made this remark because Sera isn’t elven anymore. Moreover, she can’t even understand the remark because she doesn’t speak elven, which Andruil would.
- Sera fears the void because of Chantry teachings, the exact opposite of what an elven god would believe in. More on this later.
- Iron Bull enjoys killing dragons too, but he’s probably not a god either.
It bears going into Sera’s fear of the Void and the Nothing because this is the major argument that a lot of people make. In the Fade, Sera’s fear is listed as the “Nothing.”
This comes from people not paying attention to Chantry lore. The Chantry states that once the city was blackened and the blight occurred, souls could no longer get to heaven. They are now cast into the Void, or the Nothing, unless they believe in the Maker.
Sera is a devout Andrastean and refuses to believe in Dalish gods because she is afraid of the Void/Nothing. If anything, this is more evidence that she has nothing to do with Dalish gods; she doesn’t even think they exist. It’s a character piece meant to explain why she is so fervently Andrastean. She’s afraid of her soul being lost to the void.