How long have you been together? Do you say things back to her? Does this happen at her place or yours? She probably does it because you tolerate it. Been there, done that with my ex-wife.
Once precedence has been set it is hard to undo it. If you're at her place simply say: I've shown you respect, why do you think it's okay for you to show disrespect towards me. Don't say this angry, tilt your head slightly and smirk at her as you say it. No reason to get angry. If you get angry or show emotion, she's in control.
If she apologizes, stay, if not, leave immediately and get on with your life. If she apologizes later, tell her you won't tolerate her bad behavior and are prepared to move on if she persists. You really have to mean it though.
If you're at her place, say the same thing and if she apologizes continue on. If not, politely ask her to leave. Do not try to force her to leave though as these spats could easily turn into a physical confrontation. Don't ever get physical, this could earn you a night in the slammer. Go to another room, go outside, where ever you will not be arguing with her. Listening to/engaging in this type of conversation will almost always result in you losing! :nono:
If it's bothering you now wait until you've been married to it for 15 years. You have to communicate that this behavior is not acceptable. If you continue to tolerate it this behavior it will continue. It's not your job to calm her down so stop trying. She needs to learn how to control her emotions and show that she can be respectful towards you even when she is upset.