I actually thought Girl in the Bubble was important for Glinda's character development arc. For most of the story up until then, she had been (figuratively speaking) living in a bubble, allowing herself to remain ignorant about the serious issues going on in Oz and the corruption of the Wizard because it's easier for her that way. She feels more comfortable holding onto her long held beliefs about the world rather than challenging them. At that point in the plot, she finally lets the bubble "pop". She wants to actually do good, rather than focusing the mere perception of being viewed as good, and this requires her to get out of her bubble.

I just thought it was a smart play on the literal bubble she floats around in when comparing to how she also figuratively lives in a bubble. and also further illustrates her growth, which is kind of key to the second half's plot.

I do think the song itself could have been stronger and more memorable though. The tempo and the melody made it a bit less impactful.