I am so sorry this is happening. It looks like some people never change.
I am not sure how to field the three examples, except the last one. Assuming a student from Pakistan would "blow us up" is racial profiling and discrimination. It's very unprofessional. It's not the secretary's job to determine who is a terrorist -- let the authorities determine that. At this time, we need to be compassionate and understanding of Muslims and those living in the Middle East, especially when they travel -- they are prone to so much harassment and extra attention/interrogations from the authorities, and it's all because of a few rotten apples among millions of good ones.
I'm not sure what can be done at your specific workplace. Many workplaces have harassment procedures. You can probably file complaints that way. You could also explain to the hiring staff or the secretary's manager that she is scaring clients away or making them feel unwelcome or creating a hostile environment by saying things that are racially or religiously charged, or outright racist, sexist, or bigoted. Make it clear that a secretary should be welcoming and accepting of everyone that walks through the company's doors, as well as talking about neutral things so as not to offend anyone. If this secretary cannot do that, there are plenty of other people who could take her place.
Perhaps there should be diversity/sensitivity training for all personnel where you work. They have that at my company; we have a diversity workshop every year. It is geared toward celebrating the differences between people, and accepting others and their differences as valuable and enjoyable. It sounds like the assistant has received no such training.
If you are in management, encourage those under you to come to you if they are ever made uncomfortable by a situation at work, such as hostile comments or conversations. If more than one person is complaining about the assistant, that should help to get her reprimanded or fired.
If she continues despite reprimands and your organization does nothing to stop it or take steps to terminate her, there may be nothing that can be done. You might want to try ignoring her if you can, or just make it clear that it is not okay for her to talk about that sort of thing when you're around.
Have you tried writing Dear Abby or Childfree Abby (
www.dismal-light.net/childfreeabby)? An advice columnist might have wisdom to share with you that we have not been able to cover here.
Again, I'm so sorry this is happening to you...toxic people can make coming to work every day a nightmare. I sincerely hope things get better for you.