。
She's able to speak English very well.
Literal
She [topic-は] English [object-を] very skillfully speak thing can-do.
~ことができる is the periphrastic potential — literally 'the act of speaking-English-very-well can be done.' It's slightly more formal than the simple potential 話せる; in everyday speech 話せます would do the same job more economically. Both forms coexist; ~ことができる shows up in writing, in announcements, and when speakers want to sound a bit more deliberate. とても上手に stacks an intensifying adverb with the 上手に adverbial — 'very skillfully.'