I so agree with Mrs Elliot Smith. Even when you think it's stopped you can still see traces of it occasionally. Girls have periods to get rid of the uterus lining - endometrium. Menstrual discharge is the endometrium itself, together with a little fresh blood caused by the breaking of very fine blood vessels within the endometrium as it detaches itself from the inside of the uterus. So you can see why the taste could be a little bit off arond that time of the month.....
I know with me I can 'spot' so to speak for a couple of days after my period ends. Try it again, but make sure she's well away from her time of the month and I'm sure you'll find it's not so bad.