It is possibly OK but looks a bit stiff. I wouldn't risk it, especially as the photo is not of the best quality. The connection between "H" and "e" looks a bit odd to me but I haven't done any research to see if she did sometimes sign that way. Here is one of mine that is possibly from the same kind of period:
Over contrasted/low quality photo, poor contrast on the first name/poor placement (condensed last name), skipped pen/poor ink adhesion in areas - self eliminating before authenticity concerns IMO.