Fanny Mendelssohn Hensel's "Bitte" is a strophic song. I think that Hensel is trying to portray the ambivalence of the poem through her song. Just looking at measures 9-16, measure 9 has the harmony of I, but also has some chromatic passing tones to text paint both the sweetness and the night. The next measure's neopolitan6 chord portrays the somber, mild, dream-likeness while also providing text painting for the next verse "above my live" by descending the melodic contour. The next few measures just continues the ambivalence of what has been started by providing a minor i and a V. I interpret measure 13 as just a big I chord because of the two prominent As in the melody and accompaniment. I think the rest of the notes around it are just harmonic decorations adding to the somberness of this piece which Hensel set in a major key. The next measure goes totally minor by way of a minor i6 and ii. Measure 15 returns back to the core "sweetness" of this piece by using only one minor chord and ending with a plagal cadence. How fitting for the text "unfathomably sweet night."
I think the biggest trick to performing this would be having a definite interpretation. I think you would have to pick a character that either leans more toward the "sweet" interpretation or the "somber" one. Or maybe you could have one for each verse. Because there's two sets of lyrics to the same music, the words are obviously an important part of this piece. I would also say that because of the rhythm of the song already emphasizes the chromatic notes (for instance in measure 10, the fb is a quarter note while the d is only an eighth) Hensel would probably want those notes to have more inflection. But I would suggest that the singer not "swing" too much in order to keep a nice line to the end of the consonant cadences.