Girlfriend getting a bit too comfortable around me?

When we first met she always straightened her hair before she saw me. She always dressed nice. She was always lady like. But recently its like she doesn't care anymore. She never straightens her hair anymore. Sometimes she will come see me in like pajamas. She does these really gross loud burps. And yea i'm a dude but i don't even burp i just find it rude. Idk i just kinda want her to go back to how she was around me. But now its like she doesn't really care what i think of her. Is that a good thing? Anyway to make her go back to how she was?