It does sound like your sister may not be entitled to the property but a local Probate attorney that has access to all the facts would know best. If you attorney is not available, do they have someone in the office to cover for them that can make the demand?
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The estate must be opened in the probate or similar court in your mother's area that handles decedent estates. Whoever posses the Will needs to submit it to the court.
An appraiser should be obtained to inventory and assess the value of the contents of the home. It may be possible to get a court order against your sister from removing the contents pending administration of the estate. You should contact an attorney in Arizona who can handle this since that is where the estate is.
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Your sister should not be removing property. Is there anyone else in your lawyer's office to write her a letter. She would be entitled to 1/2 of it, so what she is doing would not be considered against the law, especially if she is only taking her 1/2.