Does that freaking mean that I should start a New Game? I just completed 41 Quest and I have no saves before the 21. This game is way too broken and strange...
Well, no idea if it is fixed by a later quest because once I noticed the issue I loaded the game save from before doing that quest.
I lost some hours invested into the game but that is what I did.
There might be another way if you use the save editor.
You can open your save file and then click on "advanced" to show the switches and variables.
In the switches you can then scroll down to look for the switches for quest 21.
They should be no. 634 - 645.
Then unmark them all (but remember which ones had been marked - probably best to make a screenshot of it).
Save your file again.
Now load the edited file and go to the old lady.
With the switches being unmarked the old lady should now show her other interactions.
Complete all interactions with her you can find (at least till you get solo mode).
Then save again and edit the switches for quest 21 back to how you had them.
If it works correctly then you will know by the old lady not being locked in the cat quest conversation anymore despite you having the switches back on.
One of the other switches will then take precedence over the switches from quest 21 and hence get the old lady out of that quest.
Btw. here is a screenshot of the switches for quest 21 from a random save file of me as example:
