Texting Problem on Flip Phone

I thought maybe someone could help me with a texting problem on my wife's elderly mother's Kyocera Duraplus E4233 Sprint flip phone, which is on the TPO unlimited talk/text plan. I have a practically identical Kyocera E 4277 unactivated phone that I use, since she's 1000 miles away, to help her with problems. All is good on her phone, except she is no longer able to text because when she gets to the screen where the message is to be entered, there is always the same six numbers on what should be a blank message screen. When she hits the back button, it will erase a few of the numbers but then takes her back to the send a message window and the same thing happens over and over again, according to her. The question, to me, is how to erase the numbers that always appear on the message screen so that she can enter a new number to text? If data is turned off on her phone, would that make a difference with texting? I have had her reboot the phone,etc. with no luck. I cannot replicate her problem on my phone, so I thought someone on the forum might have some insight into this problem. Thanks.

Maybe just have her send the number message to you and that might clear it out for next time?

Maybe she accidentely created a signature?