In the beginning Patricia doesn't interest in women. After she gets enough filthy point, her lesbian feelings wake up.
No, that's not a good enough excuse. The game is terribly designed in this regard, giving you the illusion of paths that simply aren't there. She also doesn't need anywhere near as many Filthy points for most of the interactions with her son (in fact, most don't need any at all).
The game makes it seem like players can pursue both Ellie and Patricia and take a lesbian-oriented route, but you can't. And because the early requirements to even get certain scenes are high and require Filthy interactions with males, then it's just snowballing and getting worse and worse. Not to mention the way some scenes play out there is no indication to the player that some scenes even exist, because Sophia just acts like a prude and scenes end early, with no indication that there aren't enough points or anything. It isn't until you do a full Filthy playthrough that you would know certain scenes even exist (such as the alternate gym shower scene and the extended park teasing scene).
To get the latest Ellie scene you need 10 Ellie points, which means you must get EVERY Ellie point you can. You can only get a maximum of 7 points with her unless you have a Filthy score of 21, which is about
three times as much as you will get if you just focus on the girls. Because you can't get those last three points without at least 21 Filthy points, you can't actually pursue her without Sophia whoring herself out to a majority of the men along the way. And despite the fact that there is a Lesbian Temptation stat that governs things too, this doesn't even factor into several moments that are just straight-up lesbian-based interactions. And the way things are going this is only going to get worse as the game goes, because requirements get higher and higher for the girls, while chances to reach their targets become less and less. I wouldn't be surprised if Ellie is already just straight up impossible to pursue at this point now, as I imagine the latest 10-point required scenes with her are key to her being an option as a whole.
While Ellie is the worse offender, players will also just straight up miss out on several Patricia points and even more Lesbian Temptation points as well if they just pursue the girls, as several of Patricia's scenes are sneakily cut short unless Sophia is Filthy enough. And as I stated before, the game often just hides these moments entirely because there's nothing in the gameplay to directly indicate that these scenes have alternate versions unless you know, because player interaction is simply cut out as Sophia gets prudish about things and the scenes just resolve differently. To make matters worse I could access these scenes with a low Filthy score in prior versions, but it seems somewhere along the way requirements changed to make them even less attainable with a lesbian-only playthrough.
The only real way to play this so far if you want to play a lesbian-only route is to just straight up cheat and alter your save file to give yourself a lot more Filthy points from the start and then just play the content you want. Sure, it's cheating, but the system is so poorly designed and implemented it's about the only way to get through it without being frustrated.