I really like this song, but it does need to be remixed. Whether the t's and s's are too bright isn't the real issue. The vocals are simply too bright and almost distorting in the upper frequencies. I would run the instruments to a group and apply a parametric equalizer to the group and drop out the 1K slot as narrow as you can before losing the sense of mids. Then back off on the highs on the vocals. They need to sound more
natural. Her voice is already a cutting and crisp voice so you don't need the highs to capture her accurately. TRy that (don't do it too much) and see if that doesn't help. (dropping the 1K gives her voice room in the vocal range. right now her voice is fighting to stand out over the instruments. You might consider mixing it without the instruments first so the voice bass and drums (are there any?) mix right with the vocal. Then bring the instruments in just enough without crowding the vocals. That's suggestion two. Good Luck,
Rod Norman, engineer