I was just listening to it. I think the recording generally has an electronic, tinny quality. There is some distortion on a couple of her high notes. I'm not sure that there really was an equivalent of auto-tuning back then, but I may be wrong. It could be that there was a tape splice, and that the highest part was recorded in a different room and spliced in with the rest, resulting in a different sound quality there, but I rather think that it's just the sound of her particular voice up high.