I need help to find the title of a movie!

First of all sorry for my english, I am italian… The movie is from ‘40s, b/w. The plot is about a penniless girl who takes the identity of the daugher of a rich family vanished when she was a little baby. In effect she guess the right doll among many others (she see by chance that this doll is put aside, It seems to me in a strogbox…).
After I think that she regrets what she did, but my memory end here. Thanks in advance!