If you do decide to talk to the mother bear in mind that like you, she will want to believe her daughter so you may get no further than just putting your point of view accross. Doesn't sound like bullying, sounds more like your daughter just resented having to play with someone she'd already said no to and the other girl got the hump when she couldn't get them to change games for her. Next time, let your daughter be the one who decides who's company she does and doesn't want.
If you think about it, if you'd made plans with a freind then another one interupted them you'd resent them being there and theres no reason why it should be different for a child. I've done exactly as you did several times and the result is generally the same.