Maybe she tried to convince Teach to forget about revenge for Xebec's death, but Teach refused and went off to sea as a kid, hence those drawings Oda made of Teach crying alone at night, before he was eventually found by Whitebeard...
Or that Eris lost Teach during her escape from God Valley and Whitebeard found him and decided to raise him in memory of Xebec, knowing Eris would not survive if the government learned that she had Xebec's kid, probably labeling him as having 'demon blood', much like what almost happened with Portgas D. Rouge and Ace.