I used to watch an old TV show for teens in which a girl got soaked in some stuff that fell off a truck (it was in barrels). And from that point, she could melt and slide under doors and reform in her original shape. There was also a girl (her sister?) that wanted to figure out how she could melt and reform her shape, there were also other people that are the creators of the stuff in the barrels and they wanted to get her to silence her or something (it was a long time ago :) Please help...
It's The Secret World of Alex Mack, I remember some episodes so I instantly recognized the series you were referring to, although I didn't remember the title.