Hi J.!!
I am so sorry to hear about your Mom's diagnosis and prey that she comes through the treatments well.
I know exactly the situation you are in. My Mom was diagnosed with lung cancer in April of this year. I live 240 miles away from her, have a 4 year old, I'm a full time student, and a newlywed. Unfortunately my Mom lost her battle on December 1st just 3 weeks ago. What I did was spend as many weekends as I possibly could with her at her home, that was all I was able to do and be able to keep some kind of normalcy for my daughter. My Mom knew that I was doing the best I could to spend as much time with her as I could. Like you, my Mom was always there for me, she was my best friend.
I know that you don't have the ability to be in a different state a few weekends a month. Maybe you can spend a week a month with her while your husband keeps the kids with him so they are still doing their normal routines. Maybe a very trust worthy friend can help you during the time you are with your Mom. I don't think that I would take the children away from their normal routines to go to Colorado for an extended period of time. Depending on their ages, they would miss out a lot on school and other activities.
I know this is a hard decision. I also know that you will do what you know in your heart is the right thing to do for your family.
In my prayers!!
L.