In the book Uncle Tom's Cabin why does Eva make Henrique promise to try and love Dodo?

Henrique is fond and fascinated with Eva. She uses her gentle charm to appeal to any compassion he might have, "And you have taken Dodo away from all the friends he ever had, and now he has not a creature to love him;—nobody can be good that way." Finally she asks that he treat Dodo well for her sake,

"At any rate," she said, "dear Cousin, do love poor Dodo, and be kind to him, for my sake!"