OK,
So that bar is just too small. Simple as that. You might get the same effect using the old bra from your 158b
For the 168E measure her underbust, then go up 1 band size and down 1 cup size. So if she is a 32E from measurements, got for a 34DD.. (Science bit : Cup size is linked to band size. So the width of an E cup on a 36 inch band is wider than an E cup on a 30 inch band. Going down a Cup size and up a band size will give a better overall fit)
Wires can be removed from Bras, just pick a small hole in one end of the wire channel and it will pull out.
For Cleavage, you want to look for a push-up Bra. If she has gel or air fill breasts you wont do any damage. Unlikely even with solid boobs to be honest.
Maddie is a Gel Filled G and she can do cleavage for weeks!
HTH
K