The only one that comes to mind is escaping the MU in Crossover
. Not a particularly happy ending, but not an unhappy or bittersweet ending either.
Her taking over the station at the end of the series was sort of happy back-to-business-as-usual sort of ending, sandwiched between leaving Odo with his people and mourning the loss of Sisko with Jake at the very end.
She's just not a happy ending sort of character.