A lot of people seem to think she lipsynched that portion for the reason that her lips aren't really making the shape you would normally see when you sing "tere" vs. "teru" but it's a bit weird for her to have just "messed up" during that part only, you know? IMO she just really overextended the "teru" making it sound like "tere" but it still -looked- like she was singing "teru". Usually if she actually has a track played back over her voice, it's EXTREMELY obvious and isn't just for one small part of a song but no one really ever knows
for sure.