If you're the only one named in your mother's will then, subject to a couple of exceptions (some of which will note below) you would inherit everything and your sister nothing. Personal assets generally don't have title documents that result in the transfer of those assets to someone other than under a will, like a house or bank account might. For example, your mom may have had a bank account that was owned with your sister: "Mom and Sister, Joint Tenants With Rights of Survivorship" or "Mom POD Sister". If that were the case those assets would pass to your sister on your mother's death regardless of what the will said. Personal property (tangible assets like furniture, art, jewelry, coin collection, etc.) usually aren't owned that way so that they would pass under your mother's will. So if you were the only beneficiary, they would pass to you. In some cases people set up revocable living trusts to own property and then that document would govern how the personalty would be distributed. That doesn't sound to be the case for your mother. So if you were the only heir under the will why would the attorney suggest your sharing personal assets with your sister? There might be a couple of reasons, which we'll discuss, but you should really clarify them with the attorney so you understand exactly why.

Was your sister intentionally left out of your mother's will? Was your sister noted in your mother's will as intentionally not receiving anything? If your mother were to intentionally disinherit your sister (the facts above were not clear) your mother's will should have included a mention of your sister and that she is not being named as an heir (some lawyers might use a phrase like "To my daughter Jane Doe I leave no bequests, for reasons best known to me". The purpose of such a statement or clause is to prevent your sister from claiming that the lawyer simply forgot to put her name in the will (if she were not mentioned at all). This is referred to as a "scribners' error". You should clarify this with your attorney. Thus, your attorney might have suggested or encouraged you to split some of your mother's assets with your sister to avoid a will contest (lawsuit in which your sister would challenge the validity of your mother's will). Your sister could try to challenge the will if she were left out on the basis of mistake as explained above, she could claim that your mother was not competent when the will was signed, the will was not signed properly as required under state law, or that you unduly influenced your mother (i.e., you convinced your mom to favor you and cut out your sister). If any of this is possible, giving your sister some assets, and having her sign a document typically called a "Receipt and Release", might protect you and the estate. A Receipt and Release (it is known by other names as well) is a document in which your sister would acknowledge receiving the property given to her and would give up (release) any claims against, you, the estate and the executor (which might be you too). Thus, you would have traded some assets for assurance that there will be no fights or claims.

Most importantly, your sharing assets, especially personal property that often has greater sentimental then monetary value, with your sister may help preserve the family. That is an admirable act and something that will honor your mother's memory.