1999 Subaru Impreza gas filler neck leaks

Thanks for taking this question.
The car belongs to me but my daughter has it in Vermont where she lives so I haven't seen the problem. She says the gas filler neck leaks about 2 cups of gas onto the ground when I fill the tank. In 46 years of car ownership and repair, I've never had a car do this. Is this a common problem with Subarus and what do you recommend I do to repair it most economically and effectively.
Thanks much for your reply. John