Yeats hopes for beauty in his daughter--but not too much beauty!  There is a warning here, a warning that is particularly relevant for a poet who had been entranced by Maud Gonne, whom Shaw had described as "outrageously beautiful," and whom Yeats immortalized as "a woman Homer sung," "a kind not natural in an age like this."  Too much beauty removes one from the human sphere--not unlike Romeo's description of Juliet:  "Beauty too rich for use, for earth too dear"(I.v.49).  Yeats knows that an excess of beauty is destructive--as Helen destroyed Troy, as Juliet destroyed Romeo . . . not through the woman's own fault, but through the fault of men who value woman's beauty too greatly.  Here Yeats asks that his daughter be spared a beauty that may come between her and "natural kindess," that might prevent her from finding "heart-revealing intimacy" and a true friend.  And hence his next stanza refers to Helen herself, who "being chosen found life flat and dull," and also to Aphrodite, the goddess of love, who chose for her spouse the cripple, Hephaestus:

Whereas Aphrodite suffered from "being fatherless," hence without a father to guide her, Yeats intends to be a guiding father to his young daughter.