Rant. Any advice?? Warning, it's long!

Okay so my SO has 4 siblings. The youngest being a girl. She is 4. She has 4 older brothers. She is absolutely spoiled rotten (which is fine, most kids are) that being said she is an absolute NIGHTMARE. I worked for almost 2 years in a daycare that dealt with problem children, mostly involved in CPS, and she is by far, the absolute WORST child I have EVER met. She is maniuplive, she hurts animals (purposely), shes very intelligent so she knows how and what to say to get what she wants. Example: today, while watching her and her 2 brothers (8 & 15) I had to run to the bathroom (I'm pregnant and still experiencing nausea and throwing up) so I was in the bathroom for a few minutes. I walked out to this little girl sticking stuff in an outlet. She actually pried off the cover, and was shoving stuff into it. I immediately scolded her and put her in timeout, where she PROFUSELY lied about it (which is not entirely uncommon for a 4 year old to do when they're in trouble). When her mom got there a few minutes later, I told her why she was in timeout and what had happened, and this little girl, without skipping a beat, said,"it's your fault for not watching me." And skipped away. Her mother (don't even get me started) hardly deserves to be called a mom. She pushes her children off on ANYBODY who will watch them. Her mom literally laughed and said,"oh yeah hahaha she does that all the time, kids. *shrugs*" and WALKS OUT.

I cannot stand my SO step mom and their kids. They are seriously awful. Worst part is, I know that in general its the parents fault for not correcting and disciplining their kids where they should be.

I just needed to vent, sorry the post is so long!