You did the right thing to mention her 'stash' to her. It's a bit rich for her to be buying alcohol when she is (supposedly) so poor that she can't afford food!
I agree with other posters who suggest that maybe she has a problem with booze. (And, of course, if this is true she will be very defensive about it.)
If I were you I would be a bit sneaky. When you are at her home, can't you get to see what food is in the 'fridge? (Make a cup of tea, get the milk ...?)
Certainly, don't lend her any more money. If you like to have her and her child around for lunch or dinner, continue - if you can afford it. (But it sounds to me as if she's a 'taker'.)
But do keep an eye on the situation. That's very important for the child's sake.