It is impossible to address every possible allergic reaction that people may have.
Pumpkin is a member of the squash family. The customer needs to see a doctor to determine if she is allergic to products that come from pumpkins or squash. This is in her best interest.
I assume there were other ingredients (allspice?) in the pie that might be causing the customer's allergic reaction.
Her allergic reaction to certain foods is what needs to be tested, not the ingredients in the pie. This is for her own health. If she had a true allergic reaction, she needs to know what triggered it and how to avoid foods in the future that triggered the reaction.
If she is allergic to pumpkin, she needs to go to a doctor to confirm this.
Otherwise tell her that your product is 100% pumpkin and some people may be allergic to pumpkins. I assume your product is adequately identified that a person who knows what allergies they have can determine if they need to avoid the product.
If she used flour to make the pie crust, then there could be a possibility of an allergic response, or she may have celiac disease which is not an allergic reaction.