Although she doesn't have to be receiving a social security benefit in order for you to draw an ex-spouse's benefit she does have to be at least age 62 - old enough to draw it herself if she wanted to. So if that is the case you would be eligible for ex-husband's benefits and you can call 1-800-772-1213 and make an appointment to file either over the phone or in the office.
A spouses benefit is 50% at full retirement age. If taken at age 62 it is a further 35% reduction; the closer you are to your full retirement age (find it at ssa.gov) when you file, the higher the benefit. If you could afford to live on that income you could then file for unreduced benefits on your own account when you reach your full retirement age.
Of course if you don't retire there is no point in filing since half of what you earn over $15,720 (this amount changes every year and the rule is different once you reach the year in which you reach full retirement age) would be held back in benefits. At some point your earnings would be high enough so that nothing become payable. If you wait until age 70 to collect you would receive off of whichever account would give you the highest benefit. Even though she makes more than you do doesn't mean that half of her benefit would be greater than what you would get based on your own earnings. However, social security always checks that out when a person files and presents the options.
Source: I was a social security claims rep for 32 yrs.
You can't "use her SSN" exactly. If you apply for Social Security Retirement now, you'll receive the greater of your entitlement under your earnings history or any entitlement you may have as her ex-spouse. You can't receive both and you don't get to choose which. See the SS website. Keep in mind that some of your SS Retirement may be subject to income tax depending on your other income.
You need to go into SS and talk to an agent to be sure you are getting all the facts. I would call and make an appointment so that I wouldn't have to sit there all day.
If she is collecting ss, you could collect spouse benefits based on her earnings, but you wouldn't like living on what you'd get, probably well under $1000 a month.
it is possible to use her SSN