Whats the name of this movie?

What was that movie where an old blond lady finds a mother struggling to survive at the lake/river but she thinks is a great opportunity to keep the drowning mothers child and kills her by hitting her with this tree trunk instead of saving her. She then goes on to raise this child as her own...but turns out the child now an adult finds her twin sister. Maybe it was a lifetime movie, most prob. I know it's old..prob. 90's Thanks! chicaboom80@hotmail.com

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