What does "a career bitch" mean?

[on the way]

Penny,Miranda's mother, lies to Tilly,Miranda's friend, that Miranda has got a new job in television because Penny is ashamed of Miranda who runs a joke shop .Now the three of them are having a conversation in which
Tilly says,"And what a surprise,flabbergastamoomoo!No offence, I just didn't have you down as a career bitch.More someone who mucked around in a shop."
So what does "a career bitch" mean here?Is this expression commendatory or derogatory?Any help will be much appreciated.

[Gillnetter]

Penny,Miranda's mother, lies to Tilly,Miranda's friend, that Miranda has got a new job in television because Penny is ashamed of Miranda who runs a joke shop .Now the three of them are having a conversation in which
Tilly says,"And what a surprise,flabbergastamoomoo!No offence, I just didn't have you down as a career bitch.More someone who mucked around in a shop."
So what does "a career bitch" mean here?Is this expression commendatory or derogatory?Any help will be much appreciated.

I am not familiar with the phrase but it sounds as though it refers to a woman who makes her work more important than other parts of her life. "bitch" does have a sense of being derogatory, so, I would guess that there is an indication that a "career bitch" is a woman who spends the majority of her time on her job.