How can I help my 9-month-old give up eating with her thumb?

My daughter is almost 9 months old. When I feed her she puts her thumb in her mouth to suck the food in. Even when I put finger food on the tray, she picks it up with her fingers but puts her thumb in her mouth to eat it. It's almost as if she thinks the thumb is giving her the food. I try to give her a toy to hold, but she just switches it to the other hand. She only puts in her right thumb. If you hold her hand and try to feed her, she gets angry and starts to cry. I don't know how to stop her doing this, or make her understand that her thumb is not what is giving her the food. Please help!

Your daughter is making a transition from sucking to eating and is using her thumb to approximate the sucking to which she is more accustomed. Offer her finger foods that are lumps, such as pieces of cooked pasta or cereal bits, as these are really hard to suck in with a thumb, and let her work it out with these new textures and shapes. The more you make thumb-sucking a big deal, the more likely she'll do it just to tease you. Stay back and let her work it out for herself. Make sure she gets a chance to be around for at least some family meals so she gets good models.