Are the details you share with a recruitment agency kept confidential?

I was recently hired through a third-party recruitment agency, and the recruiter who placed me in my current role often checks in with me. She’s suggested meeting up soon, and I’m curious about the confidentiality of the information I disclose to recruiters. Specifically, will anything I share get back to my employer or my company?

I’ve recently discovered that my salary is significantly lower than my colleagues, which was quite disappointing, especially considering how much I feel overworked. I’m wondering if it’s safe to discuss such sensitive topics with her.