Feeling guilty about buying someone food

I was in the city and this woman stopped me and asked if i could buy her food. I thought it’d be like 5 euro but when we went inside she suddenly went to the candy isle and continued to grab 25 euro worth of candy instead of food. I put enough away to cut it down to 16 euro and took the recipe with me but i feel like i’ve been scammed and i have a hard time getting rid of this guilty feeling because with that money i could’ve just bought candy for my younger siblings what i barely ever do. I actually wanted to walk away when she only grabbed candy and i don’t even understand why i stayed and payed for her. I’m like an anxious, nervous, guilty wreck and i can’t get rid of the feeling.