Does she know ASL? If she does not know ASL or any other sign language, then she is use to using her voice instead of signing. Don't forget that there are other deaf or hard of hearing in the mainstream schools that don't allow signing at all. She must have been conditioned to be that way without the ASL accommodation. I was one of them going to the mainstream schools with no ASL and no notetakers. I had a very difficult time not understanding the teachers and the students in the regular classrooms. I used voice but my voice box is funny and deaf accent. I learned to sign in my twenty in a deaf church where the deaf pastor taught me to sign. It lift up off my chest with no pain and no suffering after years in the mainstream schools. So maybe the nice deaf woman might have problem like that in the past. You can politely ask her if she can sign. If she said no, then you will have to find someone to sign with.