The flowers mentioned in context with the Ewell's place are geraniums, seven red ones. They connect to Miss Maudie, not Mrs. Dubose. Miss Maudie militantly and religiously cares for her garden and flowers. In fact, during the fire, those flowers were of more concern and care to her than anything else.
These red geraniums represent Mayella's deep desire to live a better life than the one she's living. These are the few items in this world that she can pour effort and care into and they will flourish for her. Sure, she could try to raise those siblings of hers, she could try to have relationships, she could try to keep a clean house, but her father always destroys those things with his drinking and fits of who knows what.
Mrs. Dubose's camillias, on the other hand, represent that she has forgiven or is haunting Jem Finch for his moment of wreckless abandon in her front yard.