.. A strand of hair

Yup. She won't give you one, naturally.

Have you found any trace of her hair somewhere else?

In the sink? Look into the sink.o

Yes. Could you get the sink to flood?

Using the tap will just let the water flow down.

There is a loose pipe downstairs. You can detach it. You need to first look into the sink before Anna will remove the pipe.

Now, clog it. ( There is a cork in the basement. With the bottles. Use the cork. )

Now open up the tap. It will flood and you get the hair.