Thanks everyone for the advice. We went to to the Apple store yesterday so she could look at the iMacs. She decided that the 21.5 inch was a good size for her. The store rep was strongly in favor of her saving the money and getting either the base model or the 4K with the standard HDD at most, if she/we thought the extra resolution would be a benefit. I appreciate that there was no attempt to up-sell, but the extra $200 was not a burden on the budget, so we placed an order last night for the mid-level 4k model with a 256 GB SSD. Should last her a very long time.