She could have been trying to do a mental search for conversation topics, or maybe she was trying to say that her situation was so normal that it didn't need explaining. I'd need some more context to tell you exactly what she meant by this, such as her facial expression, but to answer your general question, no, it isn't particularly common, and it's meaning is exactly what it means literally, unless it's being used sarcastically.

This is a rhetorical question, meaning that it doesn't require an answer. It's a way of emphasising an opinion. I would expect to hear it in the following situation: Person A: 'Let's talk about the problem with xx.' Person B: 'What's there to talk about? We've already decided there's nothing we can do. We may as well forget about it. It'll sort itself out.' Person A: 'Yes, you're right.'

It sounds like it was a joke. "What is there to talk about?" sometimes means that there is nothing to talk about. Kole is absolutely right. It isn't a very common expression.

There's a lot of situations where this expression can be said in. as an example : = Your friend did something bad to you, and he tries to open a conversation with you, then you say " What's there to talk about ?", it's express here anger. like you want to say " There's nothing to talk about, get away from me..". = You want to start a conversation with a friend, and you want him to pick up a subject.. This expression can be used for other purposes too..you only know from the context where it used.