MGMAT SC question

your thought that you must modify the word that comes after the comma only applies to modifying phrases. The part before the comma in this sentence is a complete clause, meaning it has a subject and a verb, and therefore is not describing something else in the sentence. Thus, the rule that the thing that is modified must come immediately after the comma is not in play here.

I agree that the placement of "every day" is a bit awkward, though not grammatically wrong. We could move the placement of "every day" to various parts of the sentence and still preserve the intent. If we are thinking in GMAT strategy terms, we shouldn't complain about the placement of "every day" because both options include that placement. We have to shift our focus to the variations in the choices - in this case the placement of "more than" (see this post for a discussion on that issue: use-of-the-after-verb-ing-153767.html).

As to your question on modifiers, this particular structure (comma + modifying phrase) creates an adverbial modifier, which doesn't directly modify the subject (subjects are modified by noun modifiers). Adverbial modifiers will modify the verb, another modifier or the entire preceding clause. Here, "every day watering..." modifies the entire preceding clause to show how she is the most dedicated gardner on the block.

On the GMAT, this particular adverbial modifier structure will most often include a present participle (ING form of the verb) directly after the comma, so you won't often have to deal with the awkwardness you saw here with the inclusion of "every day" before "watering".

KW