The criteria measured as skating skills for singles skating are:
• Balance and rhythmic knee action and precision of foot placement
• Flow and effortless glide
• Cleanness and sureness of deep edges, steps and turns
• Power/energy and acceleration
• Mastery of multi directional skating
• Mastery of one foot skating
The videos linked in Triple Wallie's post include a segment showing Harding building up her speed with a very long sequence of very short, laborious crossovers -- a hallmark of inferior skating skills. Beyond that, she certainly wasn't anywhere near "great" on any of the six criteria.
Here's an example (mine, not the ISU's), of Tonya Harding's Skating Skills, from her 1991 Worlds FS
And for comparison's sake, here's an example of Carolina Kostner's Skating Skills, from her 2011 Skate America FS.