We independent Dommes set our own schedules and we don't all approach our work in the same way. This includes our response times. Some of us may have other jobs, children, and other responsibilities beyond this work.

"Reasonable" is subjective. Some expect a response within an hour and others a week. Ask yourself what your needs are and then look for a good match for you.

Read her website to see if she indicates when you can expect to hear back from her. Then expect it to happen within that time frame. Don't like the time frame? Then don't contact her.

If she doesn't indicate then she likely has not created a set time for herself to respond. I wouldn't have any expectations in this case.

My time frame is 48 hours. This allows me sufficient time when I am busy with clients and other obligations. But I try to reply within a day. If someone sends a request and I happen to be sitting at my desk, you may get a reply within 5 minutes.