These are all essentially equivalent, although surely might be a bit more often used in the sense of convincing oneself that she can do it, and certainly might be a bit more often used when contradicting the doubt of another that she can do it.
Also, the changing of the order of the words is often used along with emphasis of different words to convey varying shades of meaning.
CERTAINLY/SURELY she can do it. She can CERTAINLY/SURELY do it. [Disagreeing with someone who is saying that she can't do it, or responding emphatically to someone who is asking if she can do it. However, to my mind, the use of surely is a bit less emphatic than certainly, showing a bit less certainty.]
CERTAINLY/SURELY she can DO it. She can CERTAINLY/SURELY DO it. [With the idea "if she wants to".]