Does she have old nits, or active lice? You probably know about the 1 cm rule, but just a reminder anyhow.

Another treatment method that has shown good results is overnight Cetaphil. You saturate hair with Cetaphil cleanser in the evening (you can use a squeezy tomato sauce type bottle to make it easy), comb out excess, blow it dry (no need for shower caps), and wash off in the morning.

Here's detail on the method:

http://www.andoverpedi.com/patient-education/pdfs/Nuvo-lice-treatment.pdf