Parshat Lech L'cha, 5776/2015 thoughts, belated: Sarah's choice

I got into a real shouting match with one of the other folks at Seudah Shlishit over Sarah's offer of Hagar to her husband as a "surrogate mother"--we disagreed as to whether her choice showed initiative or lack of faith.  As a feminist, I resent the accusation.  On what grounds should Sarah have had faith?  Did HaShem ever speak to her?  Did she have any reason whatsoever to believe that she herself would have a baby after she'd already entered menopause and some 10 years after Hagar had born Yishmael?  I say she had every right to laugh in G-d's face, since the way G-d had treated/ignored her for literally decades was downright insulting.  And by the way, I don't notice anyone holding it against both Leah and Rachel for having gone the same "surrogacy" route--on the contrary, they're both praised for "building the house of Israel."