Alright, that's strange... Usually, it should be save-game compatible (or more accurately, there is no practical way it cannot be compatible, due to the structure of the localizations...) However, there might be issues when you are already advanced beyond Kyre's quest in the story, just to be sure, if you are, I would recommend to try and go back to an earlier save.
Please note that the mod is in English only, I don't know what it will do if you've set the game to a different language. And just to be sure, your Player character obviously as to be female for the mod to make any difference...
Did you make any changes to the game outside of installing Workshop mods, like try to edit events on your own? If so, this might explain it - otherwise, please check the path where the mod is installed (usually) /Steam/steamapps/workshop/content/GAMEID/MODID/ you should find two folders, named English/Dialogue/York and Custom Random Events/York, in which the mod files are stored. Please check if there are two files in each of these paths.

Thank you for answering! I run the mod in English, have a female character and haven't made any changes expect installing Workshop-mods. Hel, I cant even mod and stuff like that (sadly)! ^^ Maybe it's not functioning because I am too far into her quest ot something?
I couldn't find the path you're describing, but I found this: /Steam/steamapps/workshop/content/445190/1327856060/English/Localization/
Dialogue/Dowager and DowagerDinner
Are those files the mod?

Well, actually, since only the end of her quest is really affected, I don't see any reason why it should affect the mod - but on the other hand, I haven't fully tested wwhat happens if you only install it once you're far along.
That's exactly the path I was looking for, I just wasn't sure if the numeric IDs for the game and the mod are the same on your system, so I was using GAMEID and MODID as placeholders... I suppose both of the files are in .xml format? And is there a path to /Steam/steamapps/workshop/content/445190/1327856060/Custom Random Events/York as well? In there should be two files, named exatly the same, so the mod in total has 4 files in two different folders...

I found this: /Custom Random Events/CampaignMapBritain/Dowager and DowagerDinner. All four files are in XML-format.

Well, that helps - even though I almost overlooked it, I found it - the CampaignMapBritain folder should be named York, so the path should read /Custom Random Events/York/Dowager or DowagerDinner. But I cannot see where the error occurred during the upload, as unfortunately I don't have the original file anymore (so I don't know if I can fix this), but for now, could you please try and rename the folder yourself?
If this doesn't work, let me know, I still have another idea, which is a little more complicated...

Done. I'm gonna start a new game and try it again. I've already finished Kyre's quest and most of my older savefiles are gone. :/ I'll let you know as soon as possible if your solution worked, thank you so much for the help! :D

Well, that's the reason I usually don't delete the saves, at least for a game where there is no upper limit to how many you can have...
I think this renaming should fix your issuefor now, I will probably try ad search if I have a backup of the original md file lying around somewhere on the weekend, maybe I can make an update for the mod. If you run into another problem don't hesitate to ask!

I don't delete them, I overwrite them (often without thinking first). I save A LOT and there's no patience left to write a name to a new savefile when I'm so caught up in the exciting story. :P Maybe I should think about doing that anyway for cases like this. ^^ Thank you, I will return if your solution doesn't work or/and I experience more problems. xD Hope you can make an update! :)

Well, I guess it's a personal preference what to do with these files...
Let me know how it turns out, if it doesn't work yet, I will need to think further!