I have not read all the replies. What happened to the money won't ever be known. She could file a police report with no proof it was stolen, so that is just her word and not proof.
The REAL issue is that she said she would handle it. if you step in now, you tell her you don't think she CAN handle it. If she comes to you later in the week with a request for cash, maybe $10 would be okay, but I probably would not. How many weeks did YOU go to work or wherever with no money and whatever food you cuold scrounge at home? Most of us have done this many times. It wasn't fun but we survived just fine.
Don't infantilize her by solving her problems and making life easy for her. Let her be a REAL adult and struggle and miss a meal or two here or there. It won't hurt her and probably will help her grow up and maybe even help her not want to live at home so badly. Let her know that you believe that she can handle her life with-o you rescuing her from a minor 1 week problem. Let her know that you are PROUD that she figured out a solution by herself!! After all, she figured out how to get all the $$ to buy drugs didn't she? food money should be no big deal after that!
PLEASE let her be an adult and fix her own problem. You did NOT force her to leave her $ there. If you fix it, then she won't learn to never do it again.