Cant use the PlayStore after using a ROM

[Sicario31]

So, I have a friend and she wanted to install Android 4.4 kitkat on her Samsung S3 mini. She downloaded from this page: NovaFusion - Downloads , a room by the name "KitKat 4.4.4(SlimROM) 20140708". Im not sure what exactly she did, but now she doesnt have many apps and cant open the Play Sotre, it crashes as soon as she opens it. Is there a way to fix this? Is there a different way to change the os of the phone without using modified programs?

 

[TJA3500]

Make sure she installed the latest Gapps.
Custom Roms do not have the Google apps so you need to flash those separately.