"'It should be narcissi, I did not think of it'"
Narcissus poeticus
GNU Free Documentation LicenseNarcissus poeticus - Credit: Tigerente, Wikimedia Commons
 Narcissus is a genus of spring-flowering bulbs in the Amaryllis family; daffodils belong to this genus.

 

It is named after the figure from Greek mythology (see bookmark, p.132), as such flowers are said to have bloomed at the spot where Narcissus died; in particular, the species Narcissus poeticus is associated with the myth.

 

Diana is, of course, being facetious about the fact that Nan is besotted by her own reflection in the mirror.