The will has to be filed with the probate court in the county where your mother lived at the time of her death. Your sister can file a will caveat if she chooses. Whether she has grounds or will prevail is a different matter. The grounds for a caveat are generally limited to mental incapacity of your mother when she made the will, fraud, forgery or some type of undue influence. If the will was properly drafted by an attorney and if your mother was mentally competent at the time she made the will and barring anything else like fraud or undue influence, then it is not likely that your sister will prevail.
Reading of the will is a scene from Hollywood. I don't know many people who have a formal reading of the will any longer if a family member is the personal representative. If a bank or lawyer or some other person/entity is the personal representative, then there might be a need for it, but that does not seem to be your case.
Some states require that an heir be given notice of the filing of a will even if they are disinherited from the will. However, if you think that a formal reading might be likely to forestall or eliminate a caveat, then pay a probate attorney to do that at a meeting in which you are all present.
Wills have to be filed. It may be a crime to conceal a will and you can be compelled to file it if you do not do it. Whether you need to file a petition for probate is different and will depend on whether there are probate assets.
First off, there is no such thing as "reading" the will. A will is only enforceable once it has been submitted to the probate court for administration of the estate, and a personal representative is appointed by the Court. Since you have concerns about a sister contesting the will, the best thing to do is file for formal admission of the will to probate. Yes, I do recommend you hire an attorney, experienced in probate proceedings, in this situation.
Colorado law requires the will to be "lodged" with the probate, or district, court in the county of her residence at the time of her death. If she has left a self-proving will, then your sister can challenge that, but she will have a heavy lift. My collegues are correct...the best way to handle this is to retain counsel and to file for formal probate. That will cost more, because of the time expended, but it will end with a final court order that will foreclose any further dispute...except of course an appeal to the court of appeals. Whether someone will do all of that will depend upon how much money is at stake. Good luck!
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