If you look at the case, it should say how long the buyer has to respond. I wouldn't do anything as long as you have sufficiently explained your position. The next move is hers. At some point, she has the option to escalate. Or she might close the case or let it expire.
I don't think that you should accept the return in all cases. Once she has opened a SNAD dispute, there is no way to change that so she pays return shipping and the original shipping. If you accept the return, you'll be responsible for shipping both ways and you will have a SNAD on your record. I don't believe she has the option to change her return request from SNAD to changed her mind, and she can't close this request and open another.