Allergy shots/food cross reactivity

Hi! 

I was diagnosed with a birch pollen allergy. I find I am having allergic reactions to onions, nectarines, and other foods that cross-react with birch pollen.

The nurse at the allergist said allergy shots for the birch pollen issue would not help with food cross-reactivity. Is this true? 

I felt like they were just trying to get me off the phone. 

Thanks to all of you!