Beware the Nice Ones: Monica is generally so sweet that on the occasions she gets mad, or utilizes her angelic powers in a forceful way, it's pretty jarring.
Cute, but Cacophonic: Monica cannot sing (though in real life, Roma Downey has put out a CD of her own or two). One episode centered on how much it hurt Monica not to be able to sing the way she wanted to, to the point that it jeopardized her helping an assignment, a young adolescent vocalist played by Charlotte Church.
Heroic BSoD: When she witnesses a terrorist attack killing dozens, it sends her into a doward spiral Satan showing up to try and convince her to give fully up on Him and fall from Grace didn't help.
Turn the Other Cheek: When she realizes Kathleen sabotaged her review by delaying her, Monica asks God to forgive Kathleen and asks nothing of herself. This shows her superiors she is worthy of her current duties and even earns her a promotion.
Well Done My Child Angel: Monica alludes to this in Season 3's "Clipped Wings," saying that she's been so afraid of letting God down, she forgot about His mercy. In the same episode, she is so scared of being thrown out of God's kingdom that she begs the Angel of Angels to let her stay, even if she has to scrape gum from theater seats.
In the finale, she turns down a chance to be a supervisor in order to be Zack's guardian angel while he's in prison. Zack turns out to have been GOD in disguise and is so impressed that she was willing to pass up the opportunity for promotion to protect a supposed nobody that she earns the promotion after all.
Don't Fear the Reaper: He might be the Angel of Death, but he's passionate about people understanding that death, if you have made your peace with God, is not meant to be scary. Even for those who have not done this, he's more serious and pitying toward them than vengeful. He somewhat reluctantly explains this to Gloria: "Their final journey...is not so good."
Grim Reaper: He's the Angel of Death, and hates being stereotyped as this.
The Smart Girl: Absolutely. Her brain is almost literally a computer, due to the fact that God wanted to create an angel for the twenty-first century. In the Season 8 episode "Chutzpah," Sam Silverstein even gives her the nickname "Smart Girl."
God Was My Copilot: In the final episode, when Monica befriends him as a complete stranger.
Hero with Bad Publicity: He is framed for a deadly explosion at a school by the grief-stricken townspeople desperate for someone to blame. The explosion was actually caused by Satan, although Zack admits having been at the school the day of the tragedy. It turns out he was there to take the kids to heaven.
Secret Test of Character: When he is sentenced to life in prison, Monica vows to postpone any future assignments to protect him. This turns out to be the final test for her promotion, and she passes with flying colors.
Evil Is Petty / Villain Decay: In her first appearance, she tries to trick a man into selling his soul and nearly succeeds. In her second, she merely tries to instill doubt and fear of failure in Gloria.