how about you sit her on the toilet before she has a shower and if she doesn't do a poo say it will be ok now you have no poos in there.. and just keep it light.. ie your voice..

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love this idea .........

I was thinking at least for the time being to wash her hair over the bath, get her to hold a towel over her eyes to stop soap and water getting in, then you can wash the other bits with a wet cloth ??