GMAIL has the option to recover your password with the last known successful password, account creation date, 5 recent contacts, Other google services you use etc... You can get that option from the following
GMAIL Sign In page>Can't access your account?>Submit you email>Type correct CAPTCHA>Can't access any of these recovery options? Verify your identity by answering multiple questions about your account.>Answer those.... Done... You will be able to reset password if your details are true.
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GMAIL has the option to recover your password with the last known successful password, account creation date, 5 recent contacts, Other google services you use etc... You can get that option from the following
GMAIL Sign In page>Can't access your account?>Submit you email>Type correct CAPTCHA>Can't access any of these recovery options? Verify your identity by answering multiple questions about your account.>Answer those.... Done... You will be able to reset password if your details are true.
Depending how much information you know about her you can try to reset her account password. Go here for info on resetting the password for gmail
http://www.xinz.org/mobile/multiple-gmail-sign-in-gmail-login/