Need help finding a place where Mom AND a daughter can live, too! Does a place like this exist?

I have found when it comes to care, it is less about what exists, and more about what are you willing and able to pay for. Money can make many things possible.

I'm sure it exists because I've known friends with that arrangement in senior communities. Only one person has to be over 55. I'm in CO, but it must exist there too.

Do you mean you want to live in Assisted Living? I cannot imagine you would want this, but you don't give your age, so it is possible that your Mom is 90 and you are in 70s. But if you were to live with her at Assisted Living you would now BOTH be living with more elderly people than Mom would like.
You can live anywhere you like with your Mom. Consider sharing an apartment together. Consider a duplex if you can afford one, where you are living next door to one another. Consider a small home with a smaller housing in back.
I think the problem here is that your Mom needs assisted care, and if you are asking if that exists with your being able to live in the same place, I doubt it.
You could live at an assisted living facility, but would have to pay the very high fees. That is very unlikely to be affordable long term unless you have quite a lot of monetary assets.
I am uncertain exactly what your needs are, but would imagine you are familiar with all the ways of living together that exist that we know of.
I sure wish you good luck.

If your mother needs assisted living, then she needs to live in an Assisted Living facility and you can be her roommate. Lots of elders don't want to be surrounded by 'old people', yet they need assisted care. I know of no other situation where a person can get caregivers on site but where old people do not live. Sorry. Realistically speaking, AL is your best bet and there are some younger folks there too. My mom's AL has a woman named Linda living there who was 50 when she moved in. She has chronic migraines and decided she needed AL, so she moved in there 15 years ago and still lives there nowadays. I will say, this ALF looks nothing at ALL like a 'nursing home' but more like an upscale hotel. You'd just have to look around and scope out all the ALs in the area to get a feel for what you think life would be like there.

Your only other alternative is to move wherever you'd like and hire caregivers to come in to care for your mother every day. But again, a non-AL living arrangement will not give your mother the benefits of AL where doctors come TO see the residents, where meals are served, where activities and entertainment flourish, etc. Plus, in AL, the caregivers are available 24/7 at the push of a button vs. in non AL places, you'd hire a CG for a specified amount of time only, unless they're hired to live in, which is another kettle of fish.

Good luck!

I don;t know your age, but we have lots of 50 + communities here in Maryland, and I believe some offer care if needed ( probably costs more) . Can you call the aging care agency in your area and see what they know? Or a local social worker? My Aunt just bought a "condo" in one of these, and she can have help as her needs increase. But they are NOT cheap. Good luck!