Time to get a new sister or keep the same one and all of your family go for treatment. Sending videos of someone dying to attempt to control your siblings actions shows a lack of maturity on her part as well as a fear of losing control over you.
Ask your sister if she doesn't want you to ride MC's because she is knows that you are irresponsible and will certainly ride like an Ass Hat and kill yourself ?
If she says no to that then she just doesn't like motorcycles, and more importantly doesn't like the fact that you are going to do something that is outside the comfort zone of her world and also outside of where she can control you.
Three final questions Alex, before we move into final Jeopardy.
Q1. How old are you and do you still live at home?
Q2. Look at your keyboard when you send emails to your sister as soon as you input her address do the letters F & O disappear from your keyboard?
Q3. If your sister insists on searching the net so she can send you stuff to see ask her to start surfing for "Pron" for you to review, not MC Crashes
Final Jeopardy
Show your sister a picture of a KLR and tell her you plan to buy one, see the world on it and come back with a hot girlfriend, who doesn't shave her legs or pits, speaks 5 languages (reads and writes 3). You can also tell her that that the mere act of buying a KLR proves you have no fashion sense and therefore cannot be gay

, so she and her friends can stop wondering about you.
If on the other hand if you plan to buy a new sportbike as your first bike tell her she is right. You will be a rolling poppin' fresh road popsicle shortly. She should tell you what stuff she has taken from your room now so you can give it to her after you die.
Run along now,and after you can grow up enough to not share with us all the issues that your sister has about motorcycling come back and join us.