Ok, I think I found out how to fix it easy (at least on Windows, and sorry for the delay, but I just came to find this awesome game last week).
WARNING: Do a backup of your save(s) before following any instruction below. I don't take responsibility for corrupted save files that may occur for editing it things.
1- Open the .sav on a pure text editor (I used Notepad++)
2- Search for "CHARNAMEDAISY"
3- Search for the next occurrence of "is_on_quest". It will be flagged as true. change to false.
4- Search for the next occurrence of "quest_id". If it isn't null, change it to null (Warning: Mine was in null already. So if yours is not null maybe the quest may be rolling up yet. Refer to the next steps)
5- Search for the next occurrence of "quest_time_init". If it is in -1, change it to 0. Otherwise refer to the next step. (-1 means the game lost the initial condition).
6- Search for the next occurrence of "quest_time_remaining". If it is in -1, the game doesn't know when to finish it. Change it to 0 and do the steps 4 and 5 if not did them before checking this one. If it is any positive integer, maybe the quest will terminate itself after this number of turns/days.
7- Save the changes to the .sav and try to load it. If everything goes well, Daisy may be free and ready to take new tasks now. Do with her whatever do your want~
8- ???
9- Profit! :D