Level 99 - Princess of Dark Flare
It's a Korean web novel that has solo leveling vibes but with a female lead. The original publisher is crescendo.
Gates/Dungeons open on 1990's Korea causing catastrophic damage. The MC is drafted to go into the gates. At first others see her as cold, but she does grow closer to them. Then tragedy strikes, and she sacrifices herself to save a comrade. The gate closes with her in it. She eventually finds her way out to find out that 30 years have passed, and the world is completely different from how she remembers.