Amazon Fire 10 navigation bar missing, replaced with red line

My neighbor has lost the navigation bar on her Amazon Kindle Fire 10 (9th generation) and has a thick red line instead. She does not have the Gmail app. She has never enabled Alexa. "Show Mode" is unchecked, which removes the red line, but it comes back when opening any site. At the moment, she has to reboot the tablet every time she wants to change a screen. Other than a total refresh to factory specs, are there any suggestions?