The Gemora states that they were not Mekabel Geirim in the days of Shlomo. But weren't some of Shlomo's wives Mitgayer?
Eli Robbins, Baltimore, Maryland, USA
The Gemara in Yevamos 76a asks the question regarding Bas Par'oh and and answers
that since the reason they did not accept Geirim at that time was because they were converting only in order to join the "Shulchan Melachim," Bas Par'oh was accepted because she was coming from a royal table already and thus qualified for Geirus.
See also Rambam Hilchos Isurei Bi'ah 13:15-16