If she just lit them but didn't yet say the bracha, and it's still before sunset, she hasn't yet accepted Shabbat. So relight them and then make the bracha.
If she already made the bracha but it's still before sunset, she can't relight them because she accepted Shabbat. But if her husband is still home and hasn't accepted Shabbat yet for himself (he usually does that at shul), he can relight them.
If everyone around has accepted Shabbat, or if it's sunset or later, then they have to be left alone. If this happens, I've heard many people will relight them Saturday night (after Shabbos is over).