I think it’s d because that’s the one reasonable
A non-restrictive modifier add information that does not restrict who the subject can refer to (compare to "The one Marlena that enjoys many subjects" -this one restricts the subject to a specific Marlena). Here it's "who enjoys many different subjects" - it adds additional information about her, but doesn't change the referent.
Answer: When my dog died, I used humor to deflect negative emotion. It helped a lot because I really miss her
