Besart,
At 11, your sister might be interested in either JavaScript or Python, maybe even Ruby for Kids - see this post for my reason for using Python with my own kids first:
Is Python a good starter language for children?.
Scratch (from MIT) is very visual, but may feel a bit "too young" for an 11-year-old.
The great thing is that they're all free to try, and you could give her a huge head start by showing her just a few short examples in any of those languages.
You can download the source code files for Teach Your Kids to Code from the
No Starch book site for free, grab
Python for free, and see if Python might be her first choice.
Best wishes, and let me know if I can ever be of help,
Bryson