★ The shopping guide is the terminal manager of your goods and the person responsible for your goods. If she steals, it is equivalent to stealing from inside, which is absolutely unacceptable;
You also said that she was a capable person. If her theft can't be dealt with, it will happen to others again.
The boss is usually the last person to know the problem. Even you can be sure that she stole it. Please believe me, other employees must have more information than you, and they know worse. Maybe they are all waiting to see your decision.
As a newcomer, stealing when she first came shows that she is a recidivist (probably a bad habit accumulated in her previous work), which definitely shows that this person has moral quality problems;
As for your bad situation, I think it's two different things. Poor family background is not the reason for her stealing, and it is not the reason for you to give up management principles.