With Bell go to the fetish shop in New Ark and buy a cow bell, then gift it to Bell. With the science tower go to the Abandoned Base and trigger Mistrya's fight scene. If you win, there will be a third option to ask for help.
I don't know if not giving bell with a cowbell before then renovating the side of the farm ruined my progress from rescuing bell being lost and I have to start over it.
