It will help to work out what stage of labour she is in, whether her waters are broken, and how long ago (she'll know about it if she has).
She will be having contractions by now, and if they're 1-2 minutes apart then you need to get to hospital ASAP.
If there's no way to get to hospital right away, then she could try using breathing techniques to control the pain and contractions. She can take paracetamol, but nothing else. A warm bath might help too.
If she can, try and keep her walking or active (unless there are any complications - in which case lay her down).
During this time you need to remain calm for her, and do your best to get medical attention quickly.
If the baby is going to arrive before the paramedics, then the most important thing is to make sure she doesn't start pushing until she's fully dilated.
Here's a link to a birthing guide that might help you tell whether she's fully dilated or not: http://sarahvine.wordpress.com/2010/03/07/how-dilated-am-i-assessing-dilation-without-an-internal-exam/