My dad was a veteran. He divorced my mom long before he passed away. She never remarried, is she eligible for any veteran benefits?

Just a bit to add to these great responses. Your county and state will have a local VA representative that can help. Also, local VFW and American Legion has a rep that can help. Those are helpful starting places.

Check with the VA. If there was a court ordered agreement, then take copies of it to the VA. If not, you might be out of luck.

(Did you...) Ask the Veterans administration.
This would be the first step.

I am not clear on why you ask us here vs calling them directly?
Research online; ask someone to help you do the research if you cannot do it yourself.

Togo2004: Pose your question to the VA.

Talk to the VA not a random forum

I do know that your husband had to make that choice before he divorced. My husband of 20 years in military while we were married refused to assign me any benefits. So I got none. Hopefully your husband was kinder.
https://www.militarybenefit.org/get-educated/spouse/?
tel:+18005629830
Yes, a divorced spouse of a deceased U.S. military veteran may be eligible for some spousal benefits, including: 
Survivor Benefit Plan (SBP)
If the veteran opted in to the SBP and continued paying premiums, the surviving spouse may be eligible for a monthly payment or annuity. The surviving spouse can be designated as a beneficiary within one year of the divorce. 
VA health insurance
The divorced spouse may be eligible for VA health insurance if they meet the 20/20/20 rule: 20 years of marriage, 20 years of military service, and 20 years of overlap. 
Military ID, retired pay, and shopping privileges
The divorced spouse may be able to retain these benefits if they meet the 20/20/20 rule. 
Veteran's Pension
The divorced spouse may be eligible for a pension if the veteran served during a qualifying wartime period, received an honorable discharge or better, and requires assistance with activities of daily living. 
Eligibility for these benefits may be limited by factors such as the length of the marriage and the number of years of active service. The divorced spouse may need to take specific actions after the divorce to secure benefits. 
To learn more about VA benefits for divorced spouses, you can: Consult with the VA, Seek assistance from veterans' service organizations, Consult with legal experts, and Use the Veterans Benefits Management System (VBMS) to process awards. 

Absolutely might be eligible for his Social Security benefits, regardless of whether he remarried. Take her, with her documentation, to Social Security for an appointment.

Sorry to learn about the loss of your father. Did your dad ever remarry before he passed away? Contact the VA for information.

Go in person to your local VA office. They are very helpful. When I called to make an appointment, a live person actually answered the phone. They also seem to have caring veterans working there. One thing you can do that could save you some money is check with USAA insurance and see if he every became a member of that. If so, I understand that entitles and relatives, including step-relatives to use USAA.

As a military spouse I can tell you this answer is "it's complicated". The basic rule as stated above is 20/20/20. At least a 20 year marriage where 20 years overlapped with his service of at least 20 years. Contact the Veterans Administration for questions, or sometimes your local VFW or Veterans groups will have someone knowledgeable.

Found this

"A divorced spouse who never remarried may be eligible for certain VA benefits, primarily including access to healthcare through TRICARE, commissary and exchange privileges, and a portion of the veteran's military retirement pay, if they meet the "20/20/20 rule" which means the marriage lasted at least 20 years, the veteran served at least 20 years, and the marriage overlapped with at least 20 years of the veteran's service; these benefits are outlined under the Uniformed Services Former Spouses' Protection Act"

Your County should have a VA office where you can talk to someone in person. You will need Dads discharge papers and probably their marriage certificate. It will all have to do with his length of service, his rank and if he was in during wartime and maybe length of marriage. I know two men, Vietnam Vets, who use the local VA hospital as their supplimentary health plan but their wives can't so they have separate plans.

I don't claim to be an expert, but as a veteran's daughter, I've had cause to learn A LOT about VA. So, yes, a divorced spouse can apply for benefits if they haven't remarried (or, I just learned, even if their subsequent marriage ends).

Call the Veterans Benefits Administration thru VA's main number 1-800-827-1000 to quickly get the info you need. Or search the website VA.gov.

I don't know that you will find any experts on VA here. Therefore I would check for yourself and help your mom to do this. Not something you can afford to be wrong about. Google "veterans benefits for divorcees".
Good luck. Hope you will share what you learn with others.