At 58, your mom is 4 years away from qualifying for Social Security and 7 years away from qualifying for Medicare. It would be helpful for you and her to understand how much Social Security she will qualify for and what she has for health insurance between now and age 65. Her housing expenses are also key. Does she own or rent? From what I have seen, for most folks at her age, the two issues are health insurance and housing. No mortgage (a paid off house) helps. If she wants to move and downsize, the sale could provide additional retirement capital. She should do a preliminary retirement budget that accounts for all expenditures. If her expenses are $40,000 or more, her withdrawal rate will likely exceed 4 percent at least until Social Security kicks in.
Does she own a business or does she do consulting work? If she owns a saleable business, that can be counted as an asset.
If she does continue to work for a couple of years, she has the opportunity to build up her retirement in a variety of vehicles. She likely has access to better choices than just the $6,500 annual IRA contributions. There are SEPs and other plans that should be investigated.
There are a number of threads here on safe withdrawal rates and retirement calculators. She should look at a couple of the retirement calculators to see how sustainable her expenses will be.
You should be relieved that your mom is frugal and has built up this asset base. She will not be eating cat food and living under a bridge, as may be the case for many people her age that have not saved and invested wisely.