I would probably go.
On another topic, the Epi pen I wanted to share what I have done with my dd. When I RSVP I explain that dd has an Epi pen and thus I am able to stay with her to avoid the parent being put into an uncomfortable situation. This has led to me learning that one mom was a nurse, another had an older child with an Epi pen and one mom asked me to stay but asked if I could teach her how to use it for future reference. Other moms ask me for safe brands of ice cream so dd can eat it (I always send a cupcake)
I ordered the practice Epi pen from the website and taught dd how to use it, she is 7 and has been practicing for 2 years, it also comes in handy for teaching other parents.
The first round of school birthdays I stayed but as we are in our 3rd year of school I am leaving her now as many of the parents know her and are comfortable with the Epi pen. My dd is also very good about not being able to eat the same things as her friends