Street Fighter X Tekken/Elena
From Shoryuken Wiki, Marvel vs. Capcom 3 Strategy and More!
Below is a great tutorial from Links on Elena's basics that covers everything from her normals, to her optimal range, to her combo basics:
While this vid focuses on Elena and Asuka as a team, it is a good resource for some ideas on what Elena can do:
Bread and Butters
Hit Confirm Combos
Combos Into Supers