I was wondering whether the College of Creative Studies at UC Santa Barbara would be a possibility for this student. I think they have both Chemistry and Math though the student would apply to one of these programs or actually maybe have one as option 1 and the other as option 2. They do allow a student to add a second major. I am not sure if the cost would be doable or whether merit/need is given but perhaps others who are more familiar might know about the matter.
It’s possible some reachier schools might consider this student even with low EC’s. There was a mother with a mathy kid whose EC’s were not that strong. The student ended up at Oxford but posters suggested MIT and Princeton as possible schools that might overlook a lack of EC’s. Those along with the ones mentioned above such as U Chicago, NYU and CMU could be schools that the student might consider adding - or not - if the location is a factor.