I wonder how she got to Level 500 in just 3 month with the cooldown between dungeons being 7 days. She can only have gotten through 12-15 dungeons in those 3 month. So she either has a brutal exp modifier skill or has been carried through some extreme dungeons giving 30+ levels...
Or the author didnt care about the math and his own rules
Edit: It seems this C-rank dungeon gives quite a lot of exp as shown i later chapters.