Sounds like my mom. When I told her I was adopting all she could come up with were the negatives. What if there was something wrong with the child, what if this was money rip-off...you get the picture.
A wise friend said she's your mom and she doesn't want you to get hurt. She doesn't know how to say that. I think your mom is worried. She is worried about you having surgery, worried about you getting sick, etc. and mix that with guilt about how she raised you with food rewards. It would be nice if she expressed her pride in you taking this big step, but she can't say it. So carry on and do what you need to do. Your child will show his appreciation with his hugs....think of his smile the first time he can wrap his arms around you!
Your mom may never say what you want to hear. Lead by example and find a church or homeless shelter to take those Snacks. And try hugging her. She may want to but she doesn't know how to start.