Likely if all of mom's assets are in the trust then you will not need to open a probate estate. However, you need to follow certain rules when administering the trust. Therefore, I would strongly suggest that you hire a probate attorney in your area to assist the trustee do his/her job correctly!
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Unless your mother funded the trust you refer to during her lifetime with all of her property, then the will will have to be probated in order for the rest of her assets to "pourover" into the trust. As to notification of your sister, that will depend on state law which appears to be Illinois law from your question. Hopefully an Illinois lawyer, will pop in here and answer that.
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Your summary does not have enough information to answer your questions. WERE all of mom's assets titled in the trust? If so, then there is nothing to pass through probate. You should still file the Will with the court. But you would not need to open an estate or provide notice to your sister.
If there are assets that need to pass through probate, then the Will WOULD need to be admitted and your sister would need to be given notice, because she would have the right to possibly object to the Will.
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Your sister has 2 years to contest the trust. If you open a probate and admit the will (you do not need to appoint an executor), she will have only 6 months to contest both the will and the trust. There is a statute in Illinois shortening the statute of limitations.
If you are confident in the will/trust being validly executed while your mother was competent and not under undue influence, you may wish to open the probate and give your sister notice.
Does she know that mom is dead? Did she have contact with mom? Is she likely to make a problem (or even understand the purpose of giving her the statutory notice)?