Verizon/Yahoo e-mail issue


For months now I have been trying to set up my daughter's e-mail address on her iPhone, through both the built-in e-mail client and the Yahoo e-mail app.  Whenever I enter her password to set up her account I receive an "Invalid password" error message.  I can login in fine with the same password through the verizon web-mail page, but cannot login with her e-mail address on the yahoo web-mail page.  I know it is not the phone as I can login to my Yahoo'ed e-mail address on her phone.  I have tried changing her password, to no avail.  Is there anyway to get the password synchronized with the Yahoo side?  Trying to change her password on the Yahoo web site, just drops me back to Verizon's web site for the password change.