Do it the way she does it, but FUN!
Slowly push the straps off her shoulders, with lots of slow, light touching. Run your fingers lightly and slowly all over where her brastraps used to be, over her shoulders. Run your hands around the top of her back and her neck, back over her shoulders and down her chest. Graze the tops of her breasts with your fingertips.
Then, after a while, slowly peel the bra off her breasts. It'll be basically inside-out now and hanging down her belly. Cup her breasts (gently! you're just getting warmed up here!). Wrap your arms around her and crush her against you. Nuzzle into her hair and her neck.
Eventually, you can spin the bra around on her so your work is in front of you. At this point (if you can't keep her from taking it off FOR you) you can just take your time unhooking the thing.
Frankly, she's not going to give a damn how many hands you use to finally unhook the bra. You'll have impressed her with... other things. And you'll have her
full attention.
