Urgent help needed

I got a two year old I have been dealing with this for 3 weeks never had to do it before help she has lice we've done everything we can think of and can not get rid of it I'm losing my mind I feel like such a bad mom what do I do its hard to get her to stay still to comb it and I have a one year old and a new baby on the way this has got to be handled asap :'( I'm hysterical