Problem with recieving Tracfone text message help

Hey, i have a Samsung SCH-U520 Phone that im hooked up with through US. Cellular. One of my friends uses a tracfone, im not sure what make it is but i would believe its a motorola, dunno what kind its a flip phone and isnt extremely new. The problem is i can send text messages to her but she cannot send me text messages back, no matter how she puts my phone number i will never get her texts, and they also dont come late like a week later or so they just dont come at all. My texts work just find im able to text anyone else and it works good. Im perplexed because my other friend is able to send and recieve text messages from her but she uses a motorola razor phone and hooked up to US. Cellular. Can anyone give me some ideas they might have why this problem is accuring?
Thanks