I would need more information to fully answer the question, but hopefully I can provide you some information to get you started.

First, it is unclear how many siblings you have, if your mother was married when she passed, and whether your mother had a will. If she has a Will then your sister had a fiduciary obligation to follow your mother's wishes as detailed in the Will. If she did not have a Will, was not married at the time of her death, and had no other children then Colorado intestate law would have divided your mother's property equally between you and your sister.

The forgoing could be different if there was someone else's name on title (joint ownership or tenants in common) when she died or if a beneficiary deed was recorded on the property. These are non-probate transfers and are outside the scope of my answer, but suffice it to say that the Will and intestate transfer do not apply in these circumstances.

Since your sister transferred the property, I assume that she opened a probate for your mother's estate. If so, and since your name is on title, did your sister execute a personal representative deed? That is the proper type of deed to transfer ownership from an estate to a beneficiary.

Assuming your sister property opened the estate, and properly transferred the property, then you would have a solid argument that the property is yours and your sister has no rights to it. (Conversely, she would have no obligations to pay any bills related to the property.)

With all of this I am assuming your mother was a resident of Colorado at the time of her death and the probate was opened in Colorado. Given all of the assumptions I had to make, it's critical that you speak with an a attorney to discuss your options and to make sure that the property was properly transferred to you. If it was not, then when you go to sell it the buyer will not be able to obtain title insurance and the sale will fall through. You are better dealing with this uncertainty now.