Why are my text messages going through as imessages when the person doesn't have an iphone

My mother recently switched from her iphone to another phone because she got an ipad. I have the iphone 4s and when i try to text her phone now it goes to her ipad. She has her phone number unchecked under the send and receive messages on her ipad so why are the messages still going to the ipad. When I text her they are still going through as imessages instead of text messages. Anyone help!