Is Python easy to learn as compared to C/C++ for a 12year girl ?

Yes, Python is easy to learn compared to C/C++.

Reason:

The Python is a beginner-friendly programming language which is more close to human level languge or english. Thus anyone who knows english should be able to understand the syntax of Python. For a 12 year old girl it would be easier to learn and understand Python compared to C or C++. 

Though Python is more comfortable than C/C++, I suggest you start with C (don't need to become an expert in C to start Python or any other language). Because learning C language would give you the confidence of building logic. You will come to know about what libraries are, how they are used, and how they can be built. All this stuff will give you a concrete foundation for your future in computer science.
It just takes less than two weeks to learn Python, but if you want a solid foundation as a programmer, then I suggest C is the first language you should learn.

Assuming that you know the logic (sometimes referred to as the pseudocode, an intuitive interpretation of the steps/instructions that you want to code), the difficulty lies in using the syntax of a programming language to write a program that can capture your pseudocode. In comparison to C/C++, the python syntax is slightly different. So, in my opinion, All languages have the same complexity. Nevertheless, if your goal is to write a program with the minimum lines of code, Python will be the preferred language for any programmer.

Yes, as a computer science teacher I can close my eyes and say that Python is by far the most easiest programming language to learn. Many of my students prefer to learn Python instead of C/C++ because Python is a user-friendly language and has many real life applications compared to other programming languages. For example: Python libraries are extensively used in Machine Learning, Deep Learning, Data Science and Artificial Intelligence fields and also most developers prefer Python over others. Hence, it will be very easy for a 12 year old girl to learn and master python programming in a span of 3-5 months.