Unfortunately, the problem is this : originally, the first bottle of shampoo was dumped into the laundry basket twice (before and after buying the 2nd shampoo).
Later, that was changed to just mixing the two shampoos.
If that doesn't work for you, then there may well be something wrong with your playthrough up until that point.
Unless you can precisely state what your steps have been, I can't further help you : if you have used a borrowed save, it may have messed up the code ; if you are using a 3rd party mod, that very likely has messed up the code; you have missed a step somewhere playing a game that allows NO missteps, halting progress.
If you have an idea where your problem lies, please come back and say so.
I'll see you through if I can.