After escaping the mansion, you'll be able to return to her base via the passage in the lower right corner (it's a bit buggy, but just click with your mouse in that area).
First of all, thank you and secondly, if you have a lot of difficulty, there is a chest in the area before fighting any enemy with a weapon that gives a hit kill to all enemies. You don't lose anything if you use it.
Thank you very much for the tips, it's really hard to think about these details when you're doing everything alone, especially since it's my first time doing something in RPG Maker.