Allergic reaction - do I get dd up

[makedoandmend]

Posted earlier but need a bit more help. To recap dd (5) had a treatment of full marks earlier and it was only rinsed with water (at ex-h house)at first then an hour or so later a couple of shampoos wasnt shifting it at mine. It was late so I sent her to bed with hair tied up.
Just checked her after she fell out of bed and her ears are bright red and she's got an itchy scalp so obviously an allergic reaction but she's otherwise fine. Gave her a bit of antihistamine syrup to stop the itching and she's gone back to sleep.
Can I wait til morning and give the scalp a go with washing up liquid as that seems to be the only thing that shifts this stuff or do I act now with all the screaming that will entail (she hates having her hair washed)?
I'm too tired to know if I'm over or underreacting

[makedoandmend]

Oh and I've got her in my bed for the night so she's not far away.

[GobbySadcase]

Might not be an allergy. That stuff gas an alcohol base which could be causing the irritation.

I'd get it out now. Shampoo the hair dry.

[makedoandmend]

Really? You'd get her up - shes sleeping quite peacefully and isnt hot. I'm really conflicted