I have oral allergy syndrome, diagnosed when allergy tests were run before I had an operation to check I wasn't allergic to latex a few years ago.
Allergies came up I had had no idea about like apples (some I knew like horse hair). I had skin prick ones and blood tests.
I've had issues with some fruit and nuts which cause similar symptoms but I take an antihistamine daily and find more natural and unprocessed fruit/nuts trigger the symptoms more, such as nuts straight out of the nut case or from that straight into a packet, so it seems to be like something on the outside of the fruit/nut which sets the allergy off, like hazelnuts and walnuts. I'm better if they have been washed and processed but she should obviously take the appropriate advice in accordance with her allergy response.
Was the cake homemade by her or someone else at work?