Stealing or a behavior

I take care of my husband’s autistic cousin who lives with her other cousin. She knows right from wrong. The other day at lunch while I was heating my food, she got up and got another workers drinks and went back to her seat. She had her own food and drink and still took someone else’s. I made her pay for their drinks since that was all the lady had with her and would have to buy another one. I told her cousin that she stole someone else’s drink and had to pay her back for them. Her cousin says “She’s not stealing it’s just a behavior since she didn’t actually go into her bag and take them and they were sitting on the table.” I would like other opinions on this subject please. Do you still consider it stealing or is it a behavior? Her family also sugar coats when she does wrong