Hi Linus,
My Onc. has me scanned every 3 mos. unless something strange comes up between times. Sometimes you have to remind them that you're still out there. If your Mom is doing ok & not making waves, they may just have missed the follow-ups. I know this sounds awful but it does happen. MAKE SOME WAVES HONEY! Talk to her onc.
I remember when I first got my dx. I was so busy with the onc & other specialists, I had not seen my primary care in quite some time. I caught the flu & when she saw me there in the office, she looked as if she had seen a ghost. They had moved my file to deceased given my dx & the length of time since they had seen me. Looking back on it, it's kind of funny now but believe me, it was one H^&& of a shock at the time.
Never be afraid to make yourself be heard.
Good luck & my prayers are with you.
Melanie