Xopenex is still a beta-two agonist, it's still a nervous system stimulant, and in high enough doses it can cause the shakiness and fast heartbeat.
Most people with COPD find that those drugs don't work as well as the other category, which includes things like Atrovent and Spiriva.
It's a structural thing, actually, and it's because your airways in copd get kind of floppy and like to collapse on themselves and trap the air inside your lungs before you're done exhaling it. So what you do is apply extra pressure (called CPAP) onto your airways to splint them open longer and let you exhale more of the stale air!
They use it on little babies with BPD all the time -- my cousin had fun with the nasal cpap. You measure the amount of pressure you're applying by how far below the water the straw is -- it's measured in centimeters of water (which is kind of like millimeters of mercury except way more sensitive a scale -- physics geek!). Most normal people can tolerate five, going as high up as ten if her heart is strong and she's otherwise healthy could be good, but the higher up you go and the more you have to strain to blow the bubbles (even a little bit!) has bad effects on blood flow to the heart, so if she's feeling dizzy or like it's making her sick, it isn't a bad thing to stop. So if it isn't working at how deep it is, put more water in! If she's finding herself feeling dizzy or faint, pour some water out!