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I know I don't have a lot of information, but here goes, hope somebody can help me (and my sister, who watched it with me at the time) out! Please and Thank You!
So there is this guy who is cutting off women's hands(or fingers, not sure which) and sewing the hands on to his daughters (or wife's) arms so she can play piano or something. A detective finds the hands and then tries to track the killer down.
It's not a lot, but if you've seen the movie, it's hard to forget. Thank you in advance for any answers or tips!

[Purukivel]

This is a long shot: The Witch's Mirror.

[MystMoonstruck]

When the Bough Breaks (1993)
Starring Ally Walker, Martin Sheen, Tara Subkoff (film debut in double role), Ron Perlman, Robert (Rob) Knepper
IMDb synopsis:
On the Fourth of July in Houston, Texas, a teenager finds a human hand in the sewer. Captain Swaggert is investigating the discovery of seven hands throughout several years, each one precisely severed and with a number tattooed on the palm, but as yet has no leads. Special Investigator Audrey Macleah is assigned to join the team and to give support to the investigation. When the police department receives a call from a medical doctor in an institution, Audrey visits him. There, the doctor introduces an autistic boy, Jordan Thomas to her, disclosing the seven hands that the boy has drawn on the wall. Audrey dedicates her attention to Jordan and discovers that he is connected to the serial killer.

When the Bough Breaks (1994) - IMDb

Jordan has a twin sister who supposedly died at birth. Instead, her father, who is a doctor, hid her away from everyone. He operates on her every year, replacing her hands, which were deformed at birth, with hands taken from a child, marking her years of growth.