Step-Parent Relationship Cheat?

I'm not sure it's possible. Sims only seems to take into account blood relations. You should be able to test this by making the step-mother her actual mother by setting the relationship bit. See if that cools off the romance with the girl's cousin. If it does, then I'm not sure what you can do. You can leave it like that, or wait for EA to add marriage relations to the romance restrictions.

@AuroraCelery 

In real life they would not be considered family either so a romantic interest would not be off the table. However if you prefer them not to be romantically involved use the interaction "Ask to be only friends". And do not perform any romantic interactions with them in the future.

@jpkarlsenit's attraction using a mod, sims 3-style, not the in-game romance

I'd still like for her step-mom to actually be considered her step-mom, even if it doesn't do anything about her cousin

@AuroraCelery 

I can only advice to not use Mods that interfere with gameplay in a way you don't want. And she is considered her step-mom. when you check her genealogy you can clearly see she is married to the father. There really is no such thing as a step-mom. It is just a more or less convenient way to refer to a woman that is married to a man that has children with another woman.

@AuroraCelery, biologically, a step-parent and step-child aren't related, but socially they are related.  So while biologically there is nothing wrong with  a step-brother and step-sister marrying each other when they grow up, socially it is wrong, at least in most societies today. So, even though they aren't really related, I understand your revulsion of any romantic actions 🤒 , especially since socially the Sim is like a mother to your younger Sim! 😮  .

That said, we would have been able to skip a lot of this trouble if you would have stated that you were using Mods in the first post. 🤨  Thank you for finally explaining that ! 😇  Any Mods or CC can make your game act differently, and even more so in your case since the Mod you are using affects Romance, and you are having problems with Romance in your game! 😞

Like @jpkarlsen stated, if you are getting unwanted results in your game with a Mod, then the only possible way to maybe correct it is to remove that Mod.☹️  But if you decide to do this , it is best to make sure there are no traces of that Mod in your game.  We normally advise removing the entire Mods folder to your desktop if you have more than one Mod or CC Then do the following:

1) Delete the localthumbcache.package file in your game folder.

2) Fix you game in Origin by logging in to Origin and going to your Library, right-click on The Sims 4 , and choose the option to "Repair Game".  Wait for Origin to fix all of your packs and not just the base game.

If you have just the one Mod and no others or any CC then that should be enough, but if you have more Mods/CC then you will have to test putting them back one by one and seeing if your game is fixed between each item. But if you have a lot of CC/Mods, you can do the testing with the 50/50 Method.

Normally, if the Mods or CC are outdated, (which usually happens when EA releases an update patch like they did about a week or so ago), you will have to wait for the Mods/CC creators update their items to work with EA's newest patch and then put the updated version into your game. However, since we don't know if this is the case of an outdated Mod , or if it is just how the Mod works 🤔 , then that is up to you on whether you want to continue using that Mod! 😉

Best of luck, and Happy Simming! 🥳

thank you for all the replies, but I can deal with the romance mod separately. I don't need help with that. I just want a way for the game to display that she is her step-mother again. it does exist in the game, and it used to be their relationship bit, but for some reason, it disappeared. should I divorce the father and step-mother and get them married again?

@AuroraCelery, you can try that. 🤔 🙂  There is still the chance that your game is either glitched or that there is a bug .  While I've heard of some people having problems with the family tree, I don't know if the problem was the same as yours, nor do I know  how long ago this was.  It could have been an old bug that was fixed, and old bug that wasn't fixed, or a new bug that we need more data on! 

Our bug moderator is not available this week, but should be back next week.  You can check to see if there is a bug like this already in the Bug Report section.  Here is a list of Bugs.  I found a recent one that isn't the same as yours, but does deal with Family Trees : https://answers.ea.com/t5/Bug-Reports/READ-FIRST-Compiled-list-of-reported-Gameplay-Issues/td-p/3445209#FT6

If you find a broken family tree thread that is similar and you would like to add to it, hit the "Me Too" button on the first post, and then add your info at the bottom by replying to that thread! 

Best of luck! 🤞

@AuroraCeleryI'd have to investigate it, but it sounds like one relationship is overriding the other. Similar to how "Friend" overrides "Acquaintance".

If it's something like you've started a romance (intentionally or accidentally), it might override the "step-mother" relationship and show the other instead.

It shouldn't work like that though. Relationship bits are "bits" for a reason. Family relations are different from Romance relations. Not sure how "step" works into it though. A sim can be "mother" and "Friend" at the same time.