Has she got experience? If not this could be a reason for her not getting many callbacks as yet.
I got my first job as a PA through an agency, I had no actual secretarial experience but had some sector/industry knowledge and had to go in and do various tests in the agency for them to assess my typing speed, accuracy, spelling, knowledge of applications such as Word etc...
If she makes the agency grade then she could try temping agencies as well to get more experience and if she gets a good reputation as a temp she is likely to get more work and longer assignments which could become permanent.
I've used Office Angels a couple of times in the past for temping and have got two permanent positions through them and found them great.
They will usually get in touch if they have vacancies but she should keep in touch with them, at least every week I'd say. Email is a good way too. It usually becomes clear who the agencies with good work are.
A lot though depends on the work and experience needed for the positions they have and the skills and experience your daughter has.