Am I reading this correctly? If you made $40k more in your base tax year (2017) because you had full salary (instead of pension-level payments) for six months plus you got a $10k lump sum, that would mean your original salary was about $600k.
2017 income:
[300 + (300 x 0.9) + 10] = 580
Post-2017 annual income:
600 x 0.9 = 540
Difference between 2017 income and annual income thereafter is $40,000, as you said. I’m not a math genius, but I don’t see any other way to arrive at that $40k difference.
If this is the case, you should not be expecting any financial aid at all. Of course, as you said, your daughter can try for merit money.
If I am somehow way off here …
You don’t send any kind of financial aid narrative to the admissions office with the application. You can explain special circumstances on the CSS Profile when you file it—if she is applying to schools that use the CSS profile. After aid is revealed, which would be after she is accepted, if you feel they did not take your special circumstances into consideration, then write an appeal. One page, bullet points, pleasant tone, deferential. Have it ready and send it the day after she gets the award. If it’s a school that meets 100% of need, they don’t “run out” of aid. If it’s a school that does not meet full need, then I have a sneaking suspicion your daughter’s not getting anything anyway.
For Fafsa-only schools, there’s nothing you can do. Fafsa is just for federal aid, meaning Pell grant and federal student loans. I have a hunch your daughter won’t be getting a Pell grant. Anyone can get a federal student loan, though.