Another thing that helped me with itchy domes was getting custom molds. They cost under $200 for measurement and fit and for any needed changes for the first few months. Molds and domes can be made of different materials; if one material causes an itchy sensation, the audiologist can try something else. (I really got the custom molds because I was having a retention issue in one ear, but as a side benefit, it solved the itchiness problem of the open-fit domes my aids came with as well. I occasionally feel itchiness in the ear canal now, but it’s rare, whereas it was constant with the open-fit domes. I never tried the drops, but they’re worth a shot as well.)
This is not an uncommon complaint with new aids, and the audiologist should be willing to work with her on it. Good luck!