I am a homeowner planning to rent a portion to a roommate. If I include a clause that specifies that I cannot be held responsible for any injury that she might sustain due to an accident on my premises, and she slips and falls on the stairs, will the agreement be valid in Colorado courts ?

If you have a homeowner and rent a room, you will have to add a rider to your policy to include it as rental property. And your agent can guide you to all the proper coverage for what you will need.

It will change the rate of your homeowners insurance, but if you don't and they cause a fire and burn your house down, your insurance will not pay.

I am a homeowner planning to rent a portion to a roommate. If I include a clause that specifies that I cannot be held responsible for any injury that she might sustain due to an accident on my premises, and she slips and falls on the stairs, will the agreement be valid in Colorado courts ?
I doubt it. You generally can not take away the right of a tenant. Contact your insurance agent and get insurance to cover your property as a landlord. If you do not have the correct coverage and: the house catches fire, the tenant's belongings are stolen, his car is damaged in the garage... numerous things can happen. Contact your insurance agent. ALSO, be sure your tenant has renter's insurance. Renter's insurance will kick in before your insurance does. Be sure the policy lists you as an "interested party". If the tenant cancels the policy you will be notified.