The correct option is C Irony
Irony is the expression of one's meaning by using language that normally signifies the opposite, typically for humorous or emphatic effect. It's a state of affairs or an event that seems deliberately contrary to what one expects and is often wryly amusing as a result. "The irony is that I thought he could help me."
Alliteration is the occurrence of the same letter or sound at the beginning of adjacent or closely connected words. "Slowly, Silently, now the moon, walks the night in her silver shoon."
Oxymoron is a figure of speech in which apparently contradictory terms appear in conjunction. 'bitter endearment'
Personification is the attribution of human characteristics on inanimate objects. "The flowers are dancing in the breeze."
This is ironical because the expectation is that a professional who coaches couples through rough patches would herself have a strong marriage. Hence, option C is correct and the others cancel out.