Visa application process for Irish and for British passport holders

You should submit your China visa application to the embassy or consulate in the place where your passport was issued. In your case, Dublin is all right. The application can be submitted by others instead if all required documents are well prepared. Non-Irish Passport Holders who reside or work in Ireland also need provide Residence Permit and Work Permit. If she do not have these, she needs to and better apply in UK.