Eating from a Shia

I work in an office as an accountant and there is a girl in the office who is a Shia. Sometimes she brings something from her house and gives all the staff to eat and she also eats herself. Some occassions she gives money to something to bring something for her to eat for herself and she also offers us (the staff) to eat.

So my question is, can a Muslim (Deobandi or Barailwi) eat when any Shia gives anything to eat whether cooked or brought from the shop (like chips, biscuits) etc. Is is permissible. I personally do not eat but other Muslims eat and she feels bad and says that I will not eat from Shias. Is it correct what I am doing?