In British English there are a number of idioms which capture the idea, in addition to Graham's excellent answer. 

A person who has ***given up*** is somone who ***can't be bothered*** to ***make the effort***, she's just ***let herself go***.

* Wow, she's really given up
* She just doesn't make the effort any more.
* She really can't be bothered, can she?
* She's really let herself go, hasn't she?