Mrs. Lovett in Sweeney Todd. She is cheerful and kindly, but has no problems whatsoever chopping up human bodies nor really with Sweeney's killing, and she is really only interested in improving her social standing. While not necessarily hollow, she certainly doesn't give a lot of moral considerations to her actions.
All four main characters in the Sondheim musical Follies are Stepford Smilers of one sort or another. Their masks do fall eventually, and the comparison to their younger counterparts in Flashbacks becomes painful: back then, they had a reason to smile — at least, they thought they did. (It says something that Desperate Housewives gets many of its episode titles from musical numbers in Follies.)
Violetta from La Traviata hosts the best parties in Paris and has a marvelous time at all of them! ...So her admirers think, anyway. It almost seems like she is convinced of it herself. But when the young Alfredo expresses his devotion to her, her soliloquy gives the audience the distinct impression that this isn't the first time she's thought about how empty and loveless her life is.
In Mary Mary, Mary accuses her ex-husband Bob of having forced her into this type when they were married:
"I felt like I was on some damn panel show, twenty-four hours a day. Smiling, affable, humming little snatches of song. Laughing when I didn't know the answers. But affable, affable, affable! You don't know how I longed to get up some morning and feel free for once to be depressed, to be constipated, to be boring."
Jennifer in When Midnight Strikes is a Depressed example, the perfect hostess who is smiling and keeping the party going even though she's falling apart inside. Her song 'Little Miss Perfect' makes this very clear.
Edith in The Women has one pregnancy after another, even though she hates babies and doesn't like being pregnant. She seems to do a lot more complaining than smiling, but nevertheless insists that "I'm the only happy woman you know." Perhaps she does more smiling in mixed company.
Doris Teavee in Charlie and the Chocolate Factory embodies the classical Housewife of the turn of The '60s — as Willy Wonka notes, she's "dressed for 1958!" The show is set in The Present Day...and it opened in 2013. Poor Mrs. Teavee is desperately, unsuccessfully trying to cope with/deny the truth about her Enfant Terrible son Mike, who can only be controlled by letting him enjoy all the mind-rotting electronic media he wants. Her facade is full of cracks — she's perpetually anxious, has a drinking problem, and is on even more medication than he is. As it turns out, she leaves the factory a much happier person than she is when she enters it, partially because Mike ends up in a state that she can deal with....
Glinda ends up this way in Wicked. She becomes an important political figure who must act as if she hates the Wicked Witch Of The West. In reality Elphaba was her best friend. Glinda has to keep up her happy facade even when she believes Elphaba dies. It's especially noticeable in "Thank Goodness", where Glinda spends a majority of the song sounding like she's barely able to stop herself from crying while singing about how she couldn't be happier.
Martha from The Children's Hour seems to be a sweet school teacher however she has heavy issues due to her unrequited love for her close friend Karen and general gayngst that breaks her down over the course of the play to where she kills herself.
Amneris in Aida becomes this after realizing that her fiance doesn't love her and is in love with her servant/best friend, the titular character. She sings about how her upcoming marriage is a sham—while still getting ready for her wedding.
Although he tries to seem like the stable emotional pillar of the group, the songs "Halloween" and "Goodbye Love" from RENT reveal that Mark is really one of these.
"What You Own," too.
C.B. the Red Caboose in Starlight Express: "Under the smiles and under the fun, I'm Public Enemy Number One!"
Most if not all of the missionaries in The Book of Mormon, particularly Elder McKinley. They even have an elaborate tap number, "Turn It Off", about repressing emotions they consider negative, such as memories of an abusive father, sadness over not being there for a sister dying of cancer and consequent fear of developing cancer himself, and gay feelings.