The fake Rheya tries to kill herself by drinking liquid oxygen. The liquid shown is green, viscous, and foaming and looks a bit like the monster's body fluid in Alien. Liquid oxygen is colorless, non-viscous and doesn't produce sticky bubbles.
When Kelvin gives Rheya the pill to relax, note that she takes a sip of water first and then puts the pill in her mouth. When director, Steven Soderbergh, asked Natascha McElhone if she did this as a part of her performance, as possibly a statement that if "you are created by Solaris that is how you take a pill?" Natascha was confused and informed him that was simply how she took pills.