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She didn't run fast enough to catch the bus.
Literal
She [topic-は] bus [for-に] make-it [extent of-ほど] fast didn't-run.
~ほど here marks the extent or degree to which something would have been needed: 'to the extent of being in time for the bus.' Combined with the negative didn't-run, the sentence conveys 'she didn't reach the running-speed required to make the bus.' This use of ほど for sufficient-extent is one of the trickier nuances — it sets up a degree-threshold that the action either reached or failed to reach. 速く is the adverbial form of 速い ('fast'), modifying 走る.