A single person over 65 has a standard deduction of $13,600 so anything over that she would need to file a return.
Yes, her 401K counts. The RMD may count, but it may also be taxfree. For that, you will need to look at the 1099R and any other supporting documents.
Also, if 1/2 of her social security plus other income is more than $25,000, a portion of her SS would be taxable.
**Say "Thanks" by clicking the thumb icon in a post
**Mark the post that answers your question by clicking on "Mark as Best Answer"