OP here. No one else in the family has shown any signs of lice and DD6 has only had 1-3 nits to cut out each night since (I'm sure by their location and appearance they are simply ones I've missed the night before, not a new infestation). It has taken 2-3 hrs every day but totally worth it.
So here is my expert opinion after 1 week, 4 kids and HOURS of work.
Use Lice MD it is non toxic and worked IMMEDIATELY on the live ones, also made the eggs turn a different color so I think it killed them on contact. Just be careful not to get it on clothing because it is very hard to remove (it is a silicone gel- in fact the same gel that is in Mylicon Infant Gas drops..).
I sprayed one room with the lice spray and got the worst headache & stomache ache so I stopped doing it. The smell is still lingering in that room after a ton of wiping and vaccumming too.
I stripped everyone's beds, bagged all stuffed animal type things for 1 week and vaccuumed every square inch of the house. Tossed all brushes & hair ponies and DD6's pillows. All headbands and other hair items that could not be parted with were put in the freezer for 2 days. Every family member has their own hairbrush (DD6's is kept in the freezer still lol).
I have stripped DD6's bed every morning when she wakes up and I throw it in the dryer only (other than the normal once a week washing). It stays in the dryer until bed time when we make the bed then strip it again the next morning.
I have not seen a live louse (or dead one for that matter) anywhere in our house, on our kids or on DD since day 1.
I retreated her hair with LiceMD yesterday and found no nits or signs of lice at all. I will continue her once a day check and cut process for a whole month.
My theory is that if I cut out each egg/nit I see each night there is no way for them to hatch and spread. So far so good (and proud to report that NO ONE else in her classroom or our family has developed lice after DD).
I did not like the chemical harshness of RID or the spray that they sell. I used it on DH and myself and I swear it made me sick. The rest of the kids got the LiceMD treatment with no side effects.
Good luck to all of you others out there. I am so angry I could have avoided all of this had I known the little girl who spent the night at our house (and shared a pillow with DD) had lice. Her mom still denies it, although the girl matter of factly told me she had "critters" & was sent home from school that week (DD was out of school due to tonsillectomy and had not been around any other kids but my own during that time). That little girl was pulled out of school the day after my daughter with another case of it GRRR!
I wish people would get over the stigma and WARN anyone who was exposed, its' the only way to stop the reinfestation!
OMG! A mom knowingly sent her DD to stay with you with lice!!! That is awful. You are better than me. I would have called that mom up and told her that her DD even admitted it! I called anyone and everyone that has been around DD for 3 weeks. My DD even wanted me to. She said she didn't want any of her friends to have to go thru this. Goodness, I lvoe that girl!

I also found a leave in Lice Shield spray. We will be using that from now on so, hopefully, we won't go thru this again. Has anyone had luck with this kind of product?
Lice Shield contains natural essential oil extracts of:
Citronella, Eucalyptus, Rosemary and Lemongrass.