There is pretty much I. D. involved, and one has to have the PIN number for the card to get the food paid for, but yes, really, she could give them the card and designate for them to get the food instead of her. It would be pretty stupid of her if they're not shopping for her or she's not planning on sharing the food with them, since there's only so much on the card each month. Anything they get will definitely be food she does not have for herself.
EBT allotment is done on the basis of "household" and if son and daughter in law are living in the house with this person, they either are on the card eligibility account, they are committing fraud by living there illegally (which will come to light very quickly) or there is a strict "purchase and prepare" statement that the woman would have to sign saying that although she lives in the house with someone else, she purchases and prepares her own food. It could be elder abuse, if they are demanding that she give them the card and using it while she scrimps for food, but I bet that's not the case. It may be a matter of just she didn't want to have to go to grocery store this week, so they did it for her.
It would be very easy for an eligibility check to determine if the couple is living with her, and if they are not, and they're buying the food to take to their house, as I said, she's giving away food that she is supposed to be using for her own benefit. Her choice, actually.
You say you are a friend. Do you think she is doing this voluntarily, have you discussed it with her?
If you feel very strongly about it, and want to get involved, why don't you call the fraud hotline in your state and report her? It won't get her jailed or anything, but it may get her audited and required to provide more evidence about her eligibility status. If there is suspected coercion, where the daughter and son in law are demanding that she give them her EBT card to use, this would probably show them it's not a good idea, might bring the issues to light.