[DouglasS]

I completly disagree with 'a break is a break' - if there are only two of you in the store, it's taught in retail by almost all companies that if you don't know an answer/aren't able to help a customer, ask the other person, even if they're on their break, they can just make it up afterwards. As they say 'the customer is always right', and you can't just stand there blankly and say sorry.

If this woman can't handle her own job, then just file a complaint. You're still new to your position and she should know that, it's not like its happening every single break she has. She's clearly entitled, and from what you've stated very rude and jealous that you're above her, saying thins like 'you should know', which is completely ridiculous.

You should definitely report her, as you said this isn't the first time she has played up and her behaviour has been bad, she is as you stated unmanageable, and so she is affecting your job as a manager.