You'll Like My Mother (1972)

Francesca Kinsolving, a very pregnant widow whose husband was recently killed in action in Vietnam, travels to visit her late husband's mother in a snowy Minnesota town and gets snowed in with her during a fierce blizzard. Forced to wait it out, she slowly uncovers some terrible dark secrets that her mother-in-law has been hiding, such as her psychotic other son, who has recently escaped from the asylum and is shacked up in the basement.