Although it's not required for women to accept Shabbat when they light the candles, many women do decide to do so in order to fulfill the mitzvah (commandment) of Tosefet Shabbat. Tosefet Shabbat means that we accept Shabbat several minutes before sundown. And this is a requirement by the standards of Shulchan Aruch. It's logical to assume, although a measurement is not given, that somewhere around five to seven minutes before sunset is considered a significant amount of time for a person to declare that they hereby accept Shabbat and are no longer doing any more melachah (forbidden labor).
By adding extra time to Shabbat, we show that we're not just waiting for Shabbat to come; we'll want to accept Shabbat upon ourselves. Ideally, this should be done with a verbal declaration in which a person says out loud, “I hereby accept Shabbat.” But it can also be done in one's heart and mind by saying to oneself, “I hereby accept Shabbat, and I'm not doing any more melachah.”
It's ideal to do this after a person has prayed Mincha. So you come to the Beit Knesset (synagogue), you pray Mincha, and then a person accepts Shabbat. But sometimes a person might come a little bit late to the Beit Knesset and realize that if they pray Mincha, it will already cross into sunset, and they won't be able to do the mitzvah of Tosefet Shabbat. In that instance, Hacham Ovadia says they can accept Shabbat in their mind even before praying Mincha and then still go ahead and pray Mincha afterward. But one should be mindful to have a moment in which they accept Shabbat before sunset. Shabbat Shalom.