^^^ that. ever taken a really really hot shower and gotten out right away? itches for a while.
make sure you rinse her scalp really really well, and dry it well, maybe with a fan from afar or a blow drier if you're short on time. if she is allergic to mildew or mold and happened to reach her scalp it could definitely cause some bad itching, even just mild itching if she's not allergic. im allergic to both and that happened to me i think on the second week after dreading, just from drying my hair being in a room with just an old wet towel from cleaning up a spill. and having circulating air in a room with mildewy or moldy things actually serves to distribute the spores so if you're in doubt make sure her hair is dried in another room or in the sun. at the time i would rinse my hair every day so the longer your hair is wet in that certain environment the more likelihood there is. even damp carpeting or half-full soda cans can do it.
also, built up sweat and bacteria throughout the day can accumulate so rinsing every day the first month is still a good idea if the dreads dry completely.
good luck! the only things to worry about IMO is washing well, rinsing well, and drying in a timely manner like 3 hours TOPS. if you use a fan or blow dryer (fan is best, really hot air is damaging), hit the scalp if need be by directing the air at it by hanging her head. i know all that is kind of excessive but i had a really sensitive scalp at first and it made the difference for me. all that trouble went away as it readjusted...
edit: oh. change her pillow cases more frequently in case there is built up salts/bacteria from sweat or drool. im not kidding you either lol. told you my scalp was really sensitive..