My sister in law dies without a will.

I am so sorry for your loss.  If the estate going through the Probate Court?  The value of the car will matter as well as the other details of the case. Generally the fiduciary (Administrator or Executor) can transfer title.  Here is what DMV says:
Deceased owner
What to do if a vehicle owner is deceased (Motor Vehicles Only)
Use this checklist to help you transfer the ownership when the vehicle owner is deceased (MV-843). 
For transfers made by the surviving spouse 'According to the Estates, Powers & Trust Law of New York State,' the owner of one vehicle that has a value of $25,000 or less automatically transfers to the surviving spouse. If the surviving spouse wishes to transfer ownership, they must print the decedent’s name in the “Seller’s Name (Print in Full)” section on the back of the Title and sign their name in the “Seller’s Signature” Section followed by the words “as surviving Spouse”.The ownership of one vehicle that has a value of $25,000 or less transfers to the surviving children under the age of 21 if there is no surviving spouse or the spouse is disqualified. The spouse or the legal guardian of one of the children must sign the title certificate. When the spouse or the guardian signs the title certificate, they must indicate the relationship to the deceased owner. A spouse writes the word "spouse" under the signature. A guardian writes "guardian of", and the name and the relationship of the child to the deceased owner (for example, "Charles Edwards, guardian of John Smith, son").To transfer ownership of the vehicle to another person, the spouse or guardian must complete an Affidavit for Transfer of Motor Vehicle (MV 349.1). The form must be notarized. The spouse or guardian also gives the new owner a photocopy of the death certificate or certification of death. The DMV accepts a photocopy of the death certificate or certification of death. When the new owner applies for a vehicle registration or a title certificate, they must provide form MV-349.1 and the copy of the death certificate or certification of death.For transfers made by the Executor or Administrator of the Estate: If there is more than one vehicle or there is one vehicle that has a value of more than $25,000, the vehicle or vehicles become part of the estate. You cannot use the Transfer of Vehicle Registered in Name of Deceased Person (MV-349) or an Affidavit for Transfer of Motor Vehicle (MV-349.1) to transfer the ownership.
A copy of Letters of Testamentary, Letters of Administration, or Voluntary Administrator’s affidavit from the Surrogate Court MUST be submitted together with the decedent’s title transferred by the person given legal authority in the documents to sign. The Executor or Administrator of the estate must transfer the ownership by signing the title certificate. Under the signature of the Executor or Administrator, write:  Executor (or Administrator) of the Estate of, and then enter the name of the deceased owner.  For example:  "Executor of the Estate of Mary Ann Smith".