Final answer:
Holly should use the Specific Identification method to calculate her tax basis for the shares she sold.
Step-by-step explanation:
To calculate her tax basis for the shares she sold, Holly should use the Specific Identification method. This method allows her to choose which specific shares she is selling and use the purchase price of those shares to calculate her tax basis. Since Holly hasn't maintained records to track the basis of the shares, she will need to identify which shares she sold and determine the purchase price for those specific shares.