The girl working in the clinic is Evelyn.
Jakes widow is Esmeralda.
You can find two pieces of circumstantial evidence in Esmeralda's house - that you say you found.
The third piece is a note you can find in the murder location room in the tavern.
- then you confront Esmeralda with all three and that moves the plot forward.
- or you can use pet pal and talk to some animals... which is a second path by which you can solve it.
- third being just brute force.
and you can also talk to the mortician about a sheep in a grave which will cast some additional pointers your way.
But, overall, it is not necessary to solve the quest to move forward in the game. Its just useful because you get a lot of quests, xp and loot that way.
