I work with an extremely bossy colleague. We're at the same level and do the same job but she constantly tries to boss me around and tries to tell me to do things. She seems to be able to do as she likes; we are supposed to stay in our area as we are dealing with clients that walk in but she disappears off for up to an hour at a time walking off to other departments, leaving me to deal with clients single handedly. She also tries to delegate all the less good parts of our jobs to me. Oh and butts in very rudely when I'm dealing with clients 'correcting' me (in her opinion!) and taking over my interaction.
I am an assertive person but no matter how assertive I am she continues doing it day after day, even ordering me around in front of clients. I've spoken to our manager who said 'Oh she's just a bit like that, bless her'. He seems to be happy for me to pick up the slack when she's off talking at others and is always on my back asking if X, Y and Z is done. I've asked if he'd have a word with her about her bossiness and wandering off and he said no as it would only make things awkward in the office.
How do I deal with her?