Hedrin, the leave-in overnight. Pay special attention to where the hair meets the skin and make sure you go overlap onto the skin there.
Extra behind the ears and nape of neck.
Next day, sit her at a window in daylight.
Get a pair of reading glasses unless you've perfect sight.
Buy a basic plastic nit comb.
Get some big hair clips, and section by section comb each section of hair and clip back the done ones as you go.
Have some white kitchen paper and with each combing, wipe the comb on the tissue. Look for any moving little black things. Sometimes one gets stuck in the comb.
They should all be dead.
You'll find some little patches of eggs close to the scalp. These should come away as well. Note where they are.
Then you can repeat the process in 3 days time.
If there are any live nits left, the new eggs will be laid very very close to the scalp.
Older eggs will have 'grown out' a bit further down.
There's a good chance you'll get them all if you do the first treatment very carefully.
After the follow-up they should definitely be all gone.
I've got rid of them like this a few times.