Use of THE after Verb-ing ?

This question taken from MGMAT Sentence Correction book.

a)She is the most dedicated gardener on the block,every day watering the more than 50
plants in her yard.

b)She is the most dedicated gardener on theblock,every day watering more than the 50 plants in her yard

In the above sentence (a), why is "the" used after watering . Wont the sentence be correct even without using the, say
?
She is the most dedicated gardener on the block, every dav watering more than 50 plants in her yard"
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