@Lennyb08 unfortunately, the answer is easy.
SInce there was a quit claim deed prior to his death, there was no 'step up' at his death. She assumes his cost basis. The assessed value at his death of $87,000 has no bearing because he did not own the home at his death.
A) So the cost basis is $57,000 plus whatever improvements were made over the years. If there were multiple improvements made to the same element of the home (say the roof was replaced multiple times), only the last improvment adds to the cost basis.
B) The sales price is $405,000 less any closing costs (the sales commission is normally the biggest item)
So B) - A) or aroiund $350,000 is the capital gains and there is a $250,000 exclusion as long as she lived in and owned the home for at least of the last 5 years. So there would be capital gains tax on around $100,000. (probably smaller than that since there are probably home improvments and selling costs that would reduce that figure).
