This is a question for an employee benefits lawyer.  Unfortunately, there are not a lot of opportunities to create tax-advantaged retirement programs now that will be large enough to generate significant retirement income. Hopefully she will at least have her Social Security income. 

You have some flexibility if she is willing to work a few more years and can put away the maximum allowed and some catch-up money in personal retirement accounts.  You can also make a larger severance payment when she retires, but it will be subject to current income tax and will show up on your Form 990 as a highly unusual payment for the year in which it is paid.  You will also want to be sure that it is reasonable to avoid excess benefit taxes.  You can also provide a consulting contract for her after retirement, but she will have to actually consult to avoid the excess benefit taxes.  A benefits lawyer who understands nonprofits can help explain the specific opportunities that are available.

Regrettably, this is not an unusual question.  Founders are frequently willing to go without benefits for themselves in order to make more money available for the program.  Boards should be aware of the potential and override the founders on issues like this in order to avoid the problem before it is too late.