Nah, you're missing the issue. The issue is that PATREON isn't ok with incest. Credit card processors are also pushing that issue. So the character was originally supposed to be his sister, but she wasn't really in the game yet at that point, so once it became clear that having actual incest would get the game banned permanently, Alex had plenty of time to rewrite the character.
So whereas some games can have an 'easy' mod, that basically does the equivalent of Find-and-Replace to put the incest back in, this one would require a TON of work, because the character has diverged so much from the original. AKA, she's no longer a sister, and it wouldn't be simple to make her a sister anymore.
That's why polls about an incest mod were a thing: they have to balance an potentially huge amount of work over how many people really want it. I, for example, don't care either way. If she had been a real sister and the patreon ban wasn't a thing I'd be equally as happy as the current state.