Technically Tara's mother was a witch, so it makes it a lot more awkward and disturbing to me to think a lesbian was forced to give birth to children raised to either hate their mother or themselves (and the mother obviously surrendering to self-loathing as well). 'Course it's tragic enough as it stands.
But generally speaking...people like that tend to believe sexual orientation is a choice (but will virtually never admit to the times they found their own gender attractive and desirable as either romantic or sexual partners), though sometimes they show signs like they don't really believe their own words on that (*) so I'm not certain if it's a type of self-deceit about the orientation so they feel justified on hating it (and the person). But if it's a choice, then it's not something she'd turn into as she got older, at least not inevitably. They'd instead try to surround her with Bibles, crosses, and other religious props to "keep the demons away" rather than assume she WAS a demon. Besides, it's a stretch to compare Tara's trying to hide her sexuality in making other unrelated demons invisible to the rest as well.
(*Btw, I know a guy who was abused horribly because his family thought he was gay based on his mannerisms and even just being nice, and there was an incident with a pink shirt he wore that became traumatic. He was straight, and his family easeed up--he later learned a few of them celebrated--after an angry father called his dad to say if he ever caught the boy naked in bed with his daughter again he'd kill him, and this guy said at the time he wondered why he didn't get in trouble for that. He ironically beat up on his dad--they exchanged vicious blows and he got a scar from a ring his dad wore--after his dad later called that girl whom he was in love with a slut. Because of his horrid childhood he ended up bashing some gay bashers because they reminded him of his male relatives that beat up on him because they merely suspected him of being gay, and he sympathized with those who actually were. The point being he NEVER made a choice as a kid to be gay but because of his behavior it was wrongly assumed he was, and that implies that they believe it's an inherent trait rather than a conscious choice.)
(ETA: I recall a YT vid that went viral about when a boy came out. His mother insisted it was a choice he made, but also said something along the lines that she knew even as he was born! At least IIRC. It sounds too stupid to be believable, but people often are.)