I found this site for you and seems to be solid with good information.
http://lancaster.unl.edu/pest/lice/headlice018.shtml
Studies have shown even trained professionals occasionally miss live lice because the immature lice are so small and hard to see. It is also easy to mistake dandruff or hair casts for nits. Using an electronic comb may be helpful in determining whether live lice are present.
Electronic Comb--There is an electronic comb on the market, called the Robi Comb (manufactured by LiceGuard) that will detect live head lice. It is an electronic comb with metal-coated teeth that runs on one AA battery. When turned on, a soft, high pitched hum is emitted. When the metal teeth trap live lice, the humming stops. We have used this on children with head lice and find it does detect head lice, even tiny immature lice. The manufacturer claims lice trapped in the teeth are electrocuted, but we have not always found this to be true. Unfortunately, this comb will not detect eggs. The electronic comb should only be used on dry hair and care should be taken to avoid direct contact with ears, eyes and mouth. Be sure to read and follow directions for safe use of this comb. The cost of this comb is about $30; it can be found at many pharmacies or over the internet.
Treatment Options
What probably wont work--Some home remedies include cooking oil, mayonnaise, vinegar and other combinations. Studies have shown lice can survive in hair covered with olive oil, mayonnaise and even petroleum jelly--even when it is left on the hair overnight. Shampooing with ordinary shampoo wont kill lice; lice can survive through two consecutive shampooings, even when the hair is not rinsed for an hour after the second shampooing. Lice dont drown easily. Research has shown lice can survive when immersed in water for 14 hours at 86-98 degrees F.
Insecticidal Treatments--To reduce the number of live lice on your childs head, you may want to use an insecticidal product labeled for head lice control.
Pyrethrins (permethrin): Pyrethrin products currently on the market are NIX®, RID®, A-200®, Clear® and store brands with similar active ingredients. When used correctly, these over-the-counter products are pretty safe; only a few children will exhibit minor problems such as itching, a minor rash or an allergic reaction. However, research in the U.S. has shown lice are resistant to the pyrethrin/pyrethroid products, which means live lice will still be found after treatment. As these products continue to be used, resistance will increase, making these products less and less effective.
Malathion: A product reintroduced to the U.S. market several years ago is Ovide®. It has been used in European countries for many years. The active ingredient in this lotion is malathion, an organophosphate insecticide. Lice resistant to pyrethrin products may be better controlled with this product. This prescription product has an unpleasant odor and is flammable. But, the biggest drawback to using this product is the way it is to be used. Instructions say to soak the childs hair with Ovide® and leave it on for 8 to 12 hours.
Kwell®: Another shampoo product available only by prescription is Kwell®. It has been used in the U.S. for lice for about 50 years. Head lice resistance to lindane, the active ingredient in Kwell®, has been reported in many parts of the world, including the United States. This product is less effective than many other head lice treatments, taking longer to kill adults and nymphs. Kwell® should be used with extreme caution--neurotoxic reactions, carcinogenicity in lab animals and blood disorders have been reported as a result of using lindane shampoos. Because of these adverse effects, we dont recommend Kwell®.
Hair-Clean-1-2-3®: This is a non-traditional treatment with some independent research showing it has similar or greater effectiveness to Nix®. It was studied at the Miami School of Medicine and in Israel at Hebrew University-Hadassah Medical School. Hair-Clean-1-2-3® is a mixture of anise oil (flavoring in black licorice), coconut oil and ylang ylang oil in an isopropyl alcohol carrier. It has a very strong (almost overpowering) licorice smell and it should be used with caution because the alcohol makes it flammable. Spray dry hair thoroughly and leave it for 15 minutes. Then, remove lice and nits with a metal nit comb (which comes with the product). Like other products, a second application is needed 7-10 days after the first. This product is most likely to be found in health food stores.
Effectiveness--Parents sometimes report these products are not effective and often blame resistant lice or the product. However, sometimes parents are not using these products exactly as directed on the label. The most frequent problems are:
The treatment is not repeated 7-10 days later as directed on the label. The head lice nit stage is resistant to chemicals, and the treatment must be repeated to kill lice that hatched after the first treatment.
Less product is used than is recommended on the label. Because these products are expensive, parents understandably want to save the product to treat another child or for a later treatment. It is important to use the entire amount recommended on the label. Any less can reduce the effectiveness of the shampoo. Parents may need to use more product on children with lots of hair--for example, girls with long hair.
These products should not be used like regular shampoos or hair treatments. Read and follow all label directions. If you are confused, most product manufacturers have a consumer line and will help you. The telephone number will be found on the package.
Remember, resistance has been documented with the pyrethrin/pyrethroid products. The more these products are used, the more resistance will be found. But parents should be aware that even the most effective product may not be 100 percent effective. This is why using a lice comb is so important.
Aerosols--Some aerosol insecticides are sold to kill lice on environmental surfaces, but we recommend vacuuming as a much safer alternative. Studies have shown lice are nearly always found on the host and rarely, if ever on environmental surfaces so the benefits of using these aerosols are low. Aerosol products may cause respiratory problems for sensitive individuals, especially those who have allergies.
Combing: a safe, non-toxic method of lice control--Combing is the oldest and safest method of lice control; nit combs have been found in Egyptian tombs. Combing is completely safe. When done properly, it takes time and requires patience on the part of parent and child. You can completely avoid insecticide shampoos/rinses if you comb the hair to remove lice and nits, but you must be diligent. Even if you use an insecticidal shampoo, combing is the only way to remove eggs/nits from the hair.
You poor thing! I hope that another dose of RID will do the trick. 
