Gyroscopic Investing

My sister sold a very small amount (~$5K) of various individual stocks this year.  They were all gifts from a relative and are about 30 years old.  She has no idea when they purchased or what the cost basis was.

What's the best (easiest) way to handle this?

Well, I think she would have received "stepped up basis" treatment on the date of the gift.

Thus, the basis price would presumably be the price on the date on which the gift occurred.  If the gift date is not known, you might encourage her to estimate the date and find out the stock price on that date.

That's the general approach, I think.