If you've cruised by the "Symbolism, Imagery, Allegory" section, you know that chrysanthemums are 1) a symbol of death and 2) a flower with some mixed associations for Elizabeth.
When Annie is in raptures over how great the flowers smell, for example, Elizabeth claims to disagree:
It was chrysanthemums when I married him, and chrysanthemums when you were born, and the first time they ever brought him home drunk, he'd got brown chrysanthemums in his button-hole. (1.76)
Hmm, it's not very nice to tell your daughter that you hate a smell that reminds you of her existence, is it?
It's also weird that she would say she doesn't like those flowers, given that she keeps them around the house and grabbed a bunch to stick in her apron earlier in the story. You can see "Symbolism" for more on that, but the bottom line is that Elizabeth seems ambivalent about chrysanthemums: sometimes she likes them, and other times they seem to bring up squirmy feelings and memories for her.
Late in the story, however, the smell becomes clearly associated with sadness and death. The narrator highlights the chrysanthemum's significance as a symbol of death in a description of the parlor where Walter's body was to be laid out:
There was a cold, deathly smell of chrysanthemums in the room. (2.77)
So, yeah, they're definitely not a happy symbol by that point.
Since Lawrence was careful to reference the "odour" of chrysanthemums specifically (and not just the flower itself), it might be worth nothing that smell is the sense most powerfully associated with memory.
Perhaps the title and all these references to the flower's smell have something to do with working through the past in order to move forward. Clearly, Elizabeth spent a good part of the story stewing and making assumptions about her husband's lateness based on his past behavior, but she turned out to be entirely wrong—and now she has to adjust to an entirely new reality very quickly in order to take care of herself and her kids. Whether it represents death, a painful past, or both, it's clear that confronting the "odour of chrysanthemums" requires no small share of bravery for our poor Elizabeth . . .