Ah, so you're mad because you spent your day off school by doing something your mother decided to do? Why didn't you say that sooner?
Some factors made this to be harder to deduce like your main language not being english. But anyway, analyzing this thread...
What does the process of weighting underwater have to do with this?
Why did you even bother describing the whole process, how it was in a different room than the doctor's office?
What does your sister's hair have to do with all this?
What does your sister wearing tight pants and sport bra have to do with this?
What does your sister skipping shower have to do with this?
She may be hot and may look even hottter wearing tight pants and sports bras with pony tail on underwater but, as far as I can see, have NOTHING to do about YOU being mad because your mother decided how you would spend your day off.
But we can forgive you if you post some pics of your sister. If you post her in the described outfit we will be even.