lemon juice is a natural skin lightener. I have never seen anything like that happening after using nair so I don't know if lemon juice will help, I suggest Google "skin lighting or dark marks after using nair" I hope this helps.
Some forms of hair removal, such as depilatories, use harsh ingredients to break down the hair strands. This process can leave skin stained slightly. The discoloration of the skin is an after-effect of the chemical process and will sit primarily on the top layer of the dermis. There are many skin bleaching agents that deal effectively with the discoloration. However, a natural approach will avoid applying more chemicals to already treated skin and still help to bleach and exfoliate the stain to repair skin.
Cut a medium-sized lemon in half. Store one section in the refrigerator.
Sprinkle 1/2 tsp. white, granulated sugar over the stain. This will serve as a rough texture to exfoliate skin, essentially scraping off the stains cells.
Rub the half section of lemon over the sugar. The acid from the lemon will bleach skin that does not come off with the exfoliation. Press down lightly on the lemon so skin does not become irritated or abraded. Leave the solution in place after rubbing for up to five minutes. This allows the lemon juice to bleach the area.
Rinse skin with warm water to remove dead skin cells and residue from the application.
Add additional lemon juice to skin if stain remains. Leave the juice in place for 10 minutes to further bleach the stain. Rinse off with warm water.
Apply a moisturizer to skin. This will soften the area and help skin heal.
Hope this helps :)
What do the marks look like? Also your not really suppose to use Nair on your face... But I use it on my lip... So here is what I have to say. Nair is a chemical that burns hair because the skin on your face is a lot more sensitive then other parts of your body. The skin of her face could have been damaged. When I use the Nair on my lip it swells and blisters for 2 days and then no hair for a month. (I know crappy, but its the only thing I can think of to get rid of the black fuzz.) ANYWAY!!! Try getting some body scrub and face scrub, maybe some sea salt and have her scrub her face everyday like 2 times a day to get rid of the burnt dead skin on her face. It will take awhile, but I'm sure that the skin will eventually just go away. I'm pretty sure if the marks are brown its dead skin caused from the Nair. If its purple or red those are bruises blood cells drawn to the skin surface and that you can do nothing for just put ice on it...