I can't imagine what her strong matchups really are outside of melee champs who really have no ranged to counter her when she combos in. Skarner is really the only top lane champion I can think of where she can combo in and out with little fear of any rebuttal. She was good in that very specific situation, but normally she's pretty shit top because she doesn't have the sustain, so anyone who can trade with her automatically wins.I have no experience playing Riven, but some of the arguments the posters at Team Liquid (.net) have made were pretty convincing. Her weak match-ups are champs that have sustain, such as Irelia.
So pick her to counter Skarner, but for any other situation there are better champs, even if you're looking for a melee bruiser or AD bursty champ.