* "Big girls don't cry" - This is a metaphor, comparing a woman's emotional strength to a big girl who doesn't cry. It's an idiom emphasizing the expectation of stoicism in women.
* "I'm a big girl now" - This is personification, giving the characteristic of being "big" (and therefore strong) to a woman.
* "I'm gonna walk away, yeah I'm gonna carry on" - This is synecdoche (a figure of speech where a part stands in for the whole). Walking away and carrying on are actions that represent the speaker's overall resilience and determination.
While these examples are subtle, they contribute to the song's overall message of overcoming heartache and emotional strength.