maybe offer to pay the utility bill directly or offer to call the car place directly to pay bills. it might deter her from asking for cash if you try and put your foot down that you'll help with legit expenses but not other things? i'm sorry you're going through this. just a suggestion, of course.
i've had it happen with friends who were in the throes of addiction to the point where, yeah, if they need food? i'll send a supermarket gift card or ask them what they need and pick it up for them or bring them to the market. but i wouldn't give them cash because i knew that would only lead to them asking for more cash. if they come up with excuses