。
She ran as fast as she could.
Literal
She [topic-は] [as much as possible-できるだけ] fast ran.
The everyday-register version of the same construction — できるだけ paired with the adverb 速く ('fast'). The two forms (できるだけ and できる限り) are near-perfect substitutes; choice between them is a matter of register, with できる限り feeling slightly more deliberate or formal. The structure breaks down as できる ('can do') + the limiter だけ ('only / as much as'). Combined with 限り ('limit, extent') in できる限り, it gives a similar maxing-out flavor.