My Mom is a 70 years old naturalized US Citizen, collecting pensions from SDI. How many times can she travel outside US?

As a US citizen, she is free to travel outside the US for any length of time with no affect on her US citizenship. There is no expiration on citizenship, although her passport may expire. Even so, she can get a new one at the US citizen services section at the US embassy or consulate general.

Your mothers source of income is not an issue regarding citizenship.

I wish your mother a wonderful trip and good health.

If she is collecting disability benefits they may send her a notice to get recertified. Be sure to have someone collect her mail and open any letters from disability and inform her of the contents as soon as possible as she will be denied continued benefits if she misses a doctor's appointment for recertification.