I'd recommend upgrading that Thinkpad (if needed) with a SSD and possibly more RAM, and point out that all of the changes in laptop processors over the past few years have been focused on lower power not on faster speeds - a 6 year old system would have been either Sandy Bridge i5-2xxx (meh) or Ivy Bridge i5-3xxx, either of which should be just fine. The main failing will be for gaming if it was just using the built in Intel graphics. The other things that older system wouldn't have are a touch screen and possibly huge resolution, but she's not going to find those for $500 anyway.
If you do provide any further advice on used Thinkpads, stay away from the Tx40 generation if she uses the touchpad, they were *horrible*.