I received social security payments from Mexico. Is that considered income in the US?

My mother receives social security pension payments from Mexico, but she is a US resident now. She is a retiree and receives a monthly deposit from IMSS (Social Security Administration from Mexico). Does she need to declare that income in the US and pay taxes, or are there any rules that social security income from Mexico is not taxable in the US? 

 

If it is taxable, where in TurboTax should be included? And how do we get credit for the income taxes she paid in Mexico?

 

If not taxable, how do I report it without TurboTax to calculate taxes owed?