Whether something is 'added' or 'adding' is simply a matter of choice, given that this statement is timeless. “Opportunities add to her chemicals”
“Added to her chemicals are opporunities for stress.” This expresses it as a past event. The opportunities have been added.
“Adding to her chemicals are opportunities for stress.” This expresses it as present. The opportunities are currently adding to her chemicals.
But since the statement is about a timeless truth, that is, it doesn’t refer to a specific woman, or specific chemicals or opportunities, you can use either the present or past participle as the adjective.
Student or Learner