Can't send text to one contact

[Abilene2015]

I have a new to me Samsung A10e and signed up on Mint Mobile. My last phone was a Samsung J3 on Tracfone. There is one contact that I can't send texts to but can receive texts from her and I can call her. The icon by her name has a blue dot on the lower right, and when I switched to this phone and carrier, her icon by my name also developed the blue dot. How can I fix the problem of my not being able to text her? I transferred my phone number from my old J3.
So far I've restarted my phone, deleted and re-input her contact, and cleared the text message cache. I really need to be able to text this person. Thanks for any suggestions. Brigit-Carol