We swaer by Hedrin & nitty gritty too, & use an electronic comb to detect them....its makes a noise when it hits 1....it is meant to kill them, but just stuns the little [email protected] time DD got them, I experimented to see what worked, & the only thing that actually killed 1, was rosemary oil, which is an aromatherapy repelant for them.
from what you say, it does sound as if your Mum could well of been cleared of them, but has then caught them again???...........
What works for DD is Hedrin & a thorough section by section combing with nitty gritty to clear them, & then vosene shampoo, followed by a finally rinse of vinegar with added rosemary oil (1/3 of a bottle added to a bottle of vinegar (vinegar breaks down the glue that attaches the eggs to the hair, so makes the eggs easier to shift)
then spray hair with Vosene nit repellant detangling spray......again with a 1/3rd of a bottle of added rosemary oil.......comb through with nitty gritty again.....& dry/style as normal..........you also need to do the whole family & anyone in close contact at the same time.......some people can have them without itching
repeat Hedrin etc for EVERYONE a week later to kill of any stragglers that have hatched since first dose
& from then onward continue with vinegar/rosemary final rinse.....doesn't smell when dry & leaves hair lovely & shiny & easy to style.........also continue with the Vosene repellant detangling spray with the added rosemary.
DD has only ever had them 3 times, despite being around kids that get them constantly.....she caught them again recently after I got a bit blase' & didn't worry when I couldn't find the Rosemary to add to a new bottle of spray & vinegar......... worst I've seen her with & this has worked to clear them r from both her & me .....
DH surprisingly didn't get them....interesting as he uses a medical shampoo (Capasal Theraputic Shampoo) that smells exactly like the old coal tar shampoos we had as kids....when headlice just didn't happen as much as they do now
good luck
now you've got me scrattting again