My friend is allergic to mushrooms, will broth with them boiled in it and taken out lead to a reaction?

Allergy to mushroom: While cooking a food may change and reduce its ability to trigger an allergic reaction, this can vary; someone with an extreme sensitivity to mushroom could react to minute amounts of mushroom protein remaining in the broth. Not knowing the severity of your friend's allergy, you have to assume that eating the broth could lead to a dangerous anaphylactic reaction. It should be avoided.