Why does minecraft keep crashing? - 2

I downloaded minecraft for my 9 year old cousin, it works fine and all but it keeps crashing over and over. It's the 1.7.9 version. First of all, her sister's computer (the one i downloaded minecraft in) is really messed up. It has a virus to begin with. Secondly, it's really laggy. I told her she has to accept the fact that if her sister's computer isn't functioning correctly, then nothing will! Is it probably because the computer is messed up that it keeps crashing? Please answer, she's really desperate to know what's going on. And she's bothering me like every 4 mintues.

Go to search bar and type: %appdata%>Roaming>.minecraft>crash-repor…
There will be a few.txt files and look at the most recent one. At the top it will say what caused the crash. Then you can look up how to fix it from that.

Maybe it's faulty or you have an old computer?

Most probably some library files may not have installed for a new version…
So you need to install the libraries which may be lzma, asm… Or update the version 1.7.9 after deleting it in your.minecraft/versions… May it helped you… If so reply to it…