It's all about your attitude toward this. If you approach this as shameful, or embarassing, that's what it will be. Are you concerned you will overstep and offend the Mom? Here's something to try. Ask the Mom if she minds if you take the step shopping. Don't mention the bra. For the child, make it a "girls day". Tell her you're going to have a day for just the two of you. Line up some special things, a movie she'll like, lunch at a fancier place than you normally go. While you are shopping, (and it doesn't have to be a blow-out, you could say, we are both going to buy a new spring dress", just go into the lingerie department and say, "Let's make this day really special for you, let's get you started wearing bras". Hopefully, this whole experience will draw you closer together. Of course, pre-teenage girls are uber sensitive about their bodies, so if she's embarassed about the whole process, just keep trying to tell her that this is what being girls together is about. If the Mom gets miffed, play dumb, just say it happened naturally when you were shopping and you didn't think it was a big deal. I wish you luck.