Are you sure your office is large enough to be covered under ADA?
Ultimately you have to be able to do your job. If for example, you are the receptionist, one of the things a receptionist generally has to do is actually show up each day. Frequent or prolonged absences, esp. if unscheduled, can create a serious business disruption.
Here's some info from the EEOC inc. what is a reasonable accomodation.
http://www.eeoc.gov/policy/docs/accommodation.html#types
I would not email her. I would make a memo to file and document everything that happened.
Take a look at your employee handbook. What does it say about sick leave, unscheduled absences, ADA accomodations, FMLA leave, etc. Make sure you follow all the rules.