I recently got to know one of my university friends is qadiani. We have an interaction on daily basis, I try my best to avoid eating with her as much as possibly I can but sometimes we have to share our edibles even if i don’t want to. Secondly, I wanted to ask that whenever we buy something sometimes she pays the bill. Someone told me that as they are not the believers of our last prophet so they are not muslims, hence they are najis. So, you cannot eat with them in a single plate or the crockery they have used should also be purified. Is it?

There is no problem in eating with them or having them pay for your food as long as there is nothing haram.

I have not read that they are kafir and najis. Qadianis are not considered to be Muslim but the question of whether they are najis is not known. If you are worried then you can practice precaution