Advice needed!

So I am breastfeeding my almost 8 month old. It's going great, however my babysitter (a family member) is overfeeding my son. Usually he will he eat a 4 oz bottle every 3 to 4 hrs when I'm not with him. Well today I dropped him off at 9 and nursed him right before I left and went to work. When I went on my pump break at 12 I called her. She had already given him 2 bottles and solid foods... during that time he also napped for an hour and a half so he was only awake at her house for about an hour and a half and during that time she gave him two bottles. I told her that she needed to push it at least 3 hrs between feeds. Well before I got there he had eaten another bottle. That's 3 bottles in 5 hrs being gone when he's supposed to eat 1 every 3-4 hrs. I'm very frusterated bc I am not able to keep my supply up to the amount she is feeding him because he doesn't eat that normally. Also I have talked to her about it several times. I explain to her that she has to pace feed him and she shouldn't offer it unless he seems hungry because my son will just keep eating and eating even if he is full and his stomach starts hurting from the over feeding. This is the 3rd time I've had to talk to her about it and she continues to overfeed. What should I do? I don't have money for a different baby sitter so what would u do in my position? TIA