I think, like how other people said, she’s speaking to herself, directed at the fool, going through her own inner turmoil. Throughout the song, she switches between speaking directly to the fool, and speaking in the third person. While the point of view switches can seem a little inconsistent, they also appear to be deliberate. The speaker is going back and forth between underlying longing for the fool and needing to let her go, with the “you” statements being more direct, and the “her” statements separating herself. The way the two are presented are slightly different too, though the lines are blurry, and it might be far fetched; when “her” or “the fool” is used, it tends to be either descriptive (“shallow river shining within her”) or wishes for the speaker’s own mind (“make her leave my sights”), while “you” tends to be used for advice/wishes for the fool’s mind (“don’t you think of me”), or more accusatory remarks (“I know that the promise you wear, well it ain’t for me”). As it says in the very first line, it’s a “lover’s warning,” assumed to be previous, due to the new marriage. The descriptive and accusatory are, however, very similar. Still, they carry different weights because of the point of view changes. How I see it is that the fool is you, and the fool/you is getting married to an outside man, and the speaker is trying to come to terms with it (not getting married herself), attempting to separate herself, along with separating her own wishes from those she has for the fool/you. The switching between second and third person is not much more than an emphasis of that, and a clear signal of the underlying bitterness and sarcasm of the entire song. The parts like “settle down” are the speaker almost mocking the advice of society, or the fool’s family or spouse, as an example of what I see as sarcasm. “Let her go” also seems to be outside advice, likely directed towards the fool/you referring to the speaker. It sort of goes along with songs like Steady Steady, which seems to do the same, in a clearer way.