Flora made a wedding dress for Angela Wexler.

Each of the residents of Sunset Towers was chosen for a reason.  One of the residents was a dressmaker named Flora Baumbach.  Angela Wexler is getting married, and since there is a dressmaker in the building, it makes sense that they would go to her for the wedding dress.

Grace Windsor Wexler was supervising the fitting of her daughter’s wedding dress from the beige velvet couch. Above her hung the two-dozen framed flower prints she had selected and arranged with the greatest of taste and care. (Ch. 3)

Grace, Angela’s mother, considers herself an expert at design.  She believes that she should have a personal role in the making of the wedding dress, because she “could have been an interior decorator” (Ch. 3).  Making a dress is not that much different, apparently.  Grace, as usual, is overly involved and sort of making a pest of herself.

It later transpires that Flora was chosen to live in Sunset Towers because she actually made Violet Westing’s wedding dress too. 

“Angela reminds you of your daughter?” the judge asked.

“Oh my, no. Angela reminds me of another young girl I made a wedding dress for: Violet Westing.” (Ch. 13)

Flora is a lonely woman.  She is divorced and lost her only daughter young.  Her mysterious past is not really so much mysterious as it is sad.  She forms a relationship with Turtle though, and is really just a nice lady.

This is a mystery with many suspects and many players.  Flora, with her mysterious past, falls mostly into the red herring category.  She is misdirection.  She is intended to seem like a suspect, because she seems like she is hiding something, but she is pretty much exactly what she appears to be.