I babysit my toddler niece regularly as I don't work Fridays and have a daughter around the same age so they play together and generally have a nice time. Niece has never stayed over as SIL doesn't like being away from her overnight.
Yesterday I had my niece and SIL was working later than normal so picked her up about 6:30.
We baked and decorated cakes in the afternoon and naturally both kids had flour, icing and whatever else all over them and in their hair etc so I put them both in the bath and washed their hair. I popped my niece in a pair of my daughters pj's.
When dear SIL arrived I explained they'd got a bit messy so I'd bathed and changed her. She didn't say much and left quite quickly.
I've had a text this morning saying she doesn't want me to babysit again for a while as I've crossed a boundary bathing her child and she would never dream of bathing a child that wasn't hers.
I am mortified and devastated to be honest. Did I really do such a terrible thing?