Cape, I think that it says a lot about this person, that she is already worried about the amount of time that is involved. That is a good thing. You know this person, so is she organized? Has she been involved in past events? Is she good with communication? I think the work thing depends on your school. If your school is one that is struggling with volunteers, and building the PTO, then her working may be a worry. If your PTO is established and runs pretty smoothly, then I don't think it would be a problem. I think it depends more on the situation you are in and the communication skills, than the overall question of a president working.
I'm in school fulltime while also doing PTO. I am in class 14 hours of the week, during the day time, and then do student teaching one full contract day. Right now, I am available from 7:45-11 on Mondays and then on most Fridays (if I don't have a seminar or a conference). My schedule was a little more flexible in the fall, which was a blessing because of so much going on. Right now, things are slow for our PTO. Our pres is stay at home, and available to the school anytime. Our VP is also stay at home, and available. We communicate thru email, and notes in our mailboxes. We try to get as many details worked out in our monthly meetings as possible. I tend to feel guilty that I am not there so much, but I do a lot of the letters that get sent home and fliers for the walls and that kind of thing. It is hard, but it seems to work for our group. We all talked about it before being elected, and I was upfront about what my availability would be. For us, it was more important that we all worked well together and got along and had the same goals in mind and none of us are the type to say, "i do more than you do".
Good luck!