Indeed, in this special case she "run on" the "don´t let he in
" in a special way (I mean, a slurring of sorts here with "he in" sung at the same time).
I think it´s because the h letter got a weak sound (to our untrained ears perhaps), not that the h it´s not there. So the ear has to get used to the way it's sung (like "hein" in the same breath - easier listened than explained, though).
And it´s not more a "heem" than a 'hein" run on (now I mean to Brazilian and Portuguese ears).
I think you can notice it better with the last kid in the following video (at 4'37"-4'38"). At least it´s what I hope, English sounds are tricky sometimes, and with music.
They use some effects to get it into the rhythm as well.https://www.youtube.com/watch?v=wapRDsO4zXI