Parenting: How to deal with my 5 year old daughter?

I would definitely talk to her. I would use a calm voice instead of yelling, she will be more likely to listen to you. Explain to her that it is not okay to take things that don't belong to her. Look at it this way: Would she like people to take things from her? If it doesn't stop, you could try talking to the school counselor. Ignore the mother, she has no right to call your daughter "disgusting". Remember, your daughter is only 5, she is not 10, young children often make mistakes not thinking about what they are doing at the time or about the consequences of their actions.