When you are looking for lice, you are actually looking for the egg sacs, also known as "nits", not for the bugs itself. The nits are white- so they will be extremely noticeable in dark hair. They look like flakes of dandruff, and will stick to the hairline.
If your child has lice, the nits (eggs) are white, and should show up very clearly in darker hair. If you are still unsure, purchase a lice comb from your pharmacy and comb the hair at the nape. This is their favorite place to hide.
You have to check the root of the hair. grab her hair gentle and look at the root. ask her if she feel anything on her head or if it feel like her hair is moving. if so lice might be near the location. or else just shampoo her hair
It should be easier to spot with dark hair. The lice eggs, called nits, will be an off white color that shows up well in dark hair. Also, if she's scratching particularly the back of her neck and head it's a good indication of lice.