It's called an "Asshole Genie" or "Literal Genie"
No matter how you word it, the being in question will warp it in the worst way for you. Asking for her protection and guaranteed safety until they leave, means that right after they leave they end up in a death trap. Or Persephone protects them and guarantees safety from herself but not from monsters she "doesn't" control.
The only thing in stories that can actually force a none fucked over deal is another being of the same power or...a lawyer or fantasy equivalent.
Here's the thing about Literal Genies. They trick people BECAUSE that person isn't specific, they take their wish literally and twist it to fill in the vague parts.
With the word "safety" as you said, she could just guarantee safety from herself. But the word "protection" doesn't work like that. You can not protect someone from one's self, it means to shield from any obvious danger period. Which if she agrees a contract to, yes she then becomes bond to protect them. This is why I used both safety and protection in that deal, to protect themselves from both her and any dangers found in the underworld until they can leave.
Next is the part where you say right after they leave they end up in a death trap, that's not possible from what we know of the dungeon and her. If they leave the area, they are no longer in her domain and will end up in a totally random area. The most she could do is set a trap that would put them right back in the underworld but that would have to be set outside the underworld and again subject to the randomness of the dungeon to be even triggered.