How to deal with rude student?

[Teacher7676]

I chose to teach adults as I struggle with behaviour management of children, and now I just have small classes and very few issues.
I teach English as a foreign language and have one young woman (around early 20s) who is just quite rude.
Luckily I have only taught her once, but may have to teach her again in the future and plus it's a very small school.
In the lesson I had her she was whispering to another student (a male student she was flirting with). I think whispering is incredibly rude, and I'm pretty sure it was something about me.
They were also not listening to what I was saying.
She seems quite arrogant. I told her a rule in English, something about using the definite article, and she replied, "Sorry but you're incorrect." Even though I'm the native speaker.
When you walk past she doesn't smile or say hi, just has a look on her face as if she's better than you.
The male student she had been flirting with was in my class, he came into my lesson late and she walked past and let out a massive snigger, and he said "Why are you laughing?"
Just get a rude and bitchy vibe from her, but I don't feel in a position to "tell off" adults.
Nobody else is rude like that, we have some who are lazy and turn up 1 hour late etc. But they aren't sly.
Just feel uncomfortable about her and dreading having to teach her again, what would you do?

If any of my students started whispering I'd stop the lesson and ask if they needed something explaining again. Sometimes they did but were too shy to ask.

Sometimes they were just chatting - and if i realised they were mates who always sat together and it happened often, i juggled up the class, sometimes under the guise of it being good to speak to other people because of accents, abilities, etc

One trick to get people really paying attention was to either stop talking and wait or to talk quietly so they really had to listen. And often another student would tell them to be quiet.

As for grammar teaching - it depends on the class and why they're having lessons, tbh. But I've always worked on the principle that speaking is the main object of learning a language and grammar is of secondary importance for the most part. Talking and vocab are the key points for me.
But i don't teach any more because i don't enjoy it.

This.

I teach on a post-graduate university course and I think you're being way too sensitive. A bit of whispering in the class and saying you're wrong about something is really not a massive behavioural issue. I don't tell my adult students off, but try to establish a good working relationship with them to get them to do well in their exams. They are usually financing the course themselves and are there voluntarily because they want to learn/get the qualification, so you can't treat them like school kids.