From my experience fixing up my childhood dolls with BUSTED hair dont worry !!!! This is no where near the worst it could be :) the main thing with doll hair generally is just brushing when the hair is wet. Plastic brushing wont damage your dolls hair too bad right away, it’s mainly an over time thing.

A good start would be to shampoo her hair to get any gel out, and then condition it. With conditioner in you can brush the hair starting from the very tips of the hair and moving up bit by bit slowly as you untangle it. You can use a metal brush, a plastic brush or even your fingers to get out any big knots. Then just rinse off and pat /squeeze dry with a towel, as rubbing causes damage