If you don't have an example, I'll be keeping her as adopted.No links but when patreon put their foot down on incest it just started with blood relations so people started doing step/adopted families and after a while patreon came down on them too.
Best option would probably be put them out as former roommates on patreon but post a script file with them as siblings here. Bit more work but is a bit safer.
If patreon complains she will be removed from the game entirely, not toned down.
(and remember that it's a very small part of the game and not advertised much so I don't think it will be a big deal, most games patreon game down on were completly about incest and it was even in the title and description)