Hi Tracey,
First let me say I'm sorry you've had to join this club (counts for care givers as well as patients). It is a scary place and it makes the caregivers feel so helpless. DH has stage 4 colon cancer, so I'm pretty familiar with what you're going through.
This place is great, but it's also fairly general - you probably ought to also hang out at the
Colon Club which is specifically for colo-rectal cancer (patients, relatives & assorted caregivers). They are amazingly knowledgeable and very patient answering questions and explaining the medical-ese and about various treatments. It's been a huge help to me!
Most likely what your mom is getting is a PET/ct - she will drink some glucose stuff and then go into an MRI-like machine which takes pics of how much of that drink was 'taken up' by the cancer cells. This tells the Dr where all the cancer is and how active it is. It's a very important management tool. and they will do regular PET/ct to compare from the initial one so they can keep tabs on the progress. Did she get a port installed? It's usually just below the collar bone - makes it easier to hook up for chemo.
How your mom reacts to the chemo depends a lot on her: her level of health otherwise, how much exercise she gets, and how much she wants to accept her treatment and not fight it. DH is still going to work every day, still going for cardio walks most days. He had a little trouble with the folfox side effects (hair thinned but didn't fall out, mostly it's the cold sensitivity in the hands and the tingling in the fingers & toes that gets you). Nausea can usually be controlled with meds like Zofran or Compazine. If she has any nausea, she shouldn't be afraid to take something, and if one doesn't work, she can take the other at the same time. Just take one every day to keep an even level in her blood stream. and if it gets bad, don't be afraid to call the dr!
Her attitude is key! and you have to work on sucking it up around her (fall apart as much as you want away from her, but don't show any fear or negative emotion around her - you don't even want the 'what ifs' and 'might nots' lodging in her mind. If you have to, just put it all out of your mind any time you're around her - the more you convince yourself things will be fine, the more she will feel that way and the more likely it is to happen. If you get all doom and gloom, it rubs off on her. She doesn't need that.
Sometimes the first round (6 months) of chemo doesn't work very well, but there are plenty of other things they can try that can work miracles. DH is on his second round and just had another PET and it was amazing! the dr was so tickled he's lowering the chemo dose and got really really excited.
Things have come such a long way from 20 years ago. Even though the folfox didn't work that well, it worked quite well enough that he was still around 6 months later to try something else, and that's a lot better than 20 years ago.
So yes, it is very scary - try not to go into the dark place of 'what if'. People manage for years and years. She will now have a new 'normal' for her life and things to keep an eye on, but it doesn't really have to interfere with things unless she wants it to.
If you have any questions about it, feel free to DM me; but really - go to the Colon Club. They have a sticky that explains nearly all of the common medical terms and procedures, and people are great for explaining various test results and drug protocols.
Hang in there.