Here's my standard response.
As new divers you probably took classes with a Jacket BCD. They're easiest to configure for your shop/training purposes and do a pretty decent job. Especially while floating you on the surface vertically. For actual diving though, a back-inflate model seems like a superior design since when horizontal the air bubble is completely on your back making it generally easier to trim out while actually diving. If you consider the 3 common types - Jacket, Back-Inflate or Backplate/Wing - 2 of 3 position all the air on your back. Must be a reason for that...A telling example is one of the low-end Jacket models - maybe a Mares or Cressi? - comes with a permanent barcode on the shoulder for inventory tracking purposes...
Also while the Pro HD is a good option for you she might like something cut for a woman instead. Both for the "girls" and also since they're generally shorter in the torso since most women are also. Which positions the integrated weights in the right spot.
For that reason, maybe consider a Pearl instead if you're set on an Aqualung Jacket. Or a Lotus if you decide back-inflate is a better option. Whatever you do - don't buy an I3. It takes a relatively simple, straighforward inflator design (schrader valve - there's one in your tires) that's been used for decades and needlessly complicates it so you can push a lever instead. And adds about 20+ failure points, custom dump valves, a custom lever system in the process. Making the only place you can get it fixed an Aqualung Dealer with a specially trained technician - and more importantly the only place to get repair parts. That's gotta cost more...
My anecdotal story is diving the 2nd day on a liveaboard trip a few years ago. The diver next to me powered up his gear and we both watched his inflator button fly across the deck. However the spring flew farther - over the railing into the water. The DM laughed, went below and came back with one he'd cut off a rental. Two cable ties later and the diver was on the same dive I was. Had it been an Aqualung he'd have been renting all week since the boat never touched land. Maybe an extreme example but it's why I stay away from anything proprietary if possible. I don't buy my own personal gear not to use it.
For only warm water, vacation diving the ZUMA is a much better option. You can add another pocket to the front strap to carry more stuff if desired, it's small, lightweight and rolls up into a bag that is small and light enough to carry on. Other similar options are ScubPro's Lighthawk or Zeagle's Covert - which at 3.9lbs. is among the lightest sold and designed to roll-up. 2013 Lighthawks are also selling for $250 at LeisurePro.com. The Covert is $439
My feeling is with your planned dive count - keeping it clean and rinsed you may never need to have it serviced. I do a lot more dives every year than you may total, abuse my gear slightly and in the last 12 years that I've owned my current BC - the only repairs it's needed was one $25 inflator hose. I more changed that also since the company has a new version for $50 with a removable inflator so you screw on a standard garden hose to flush it. It hasn't seen the inside of a shop in at least 8 years. I took it in once for a end of warranty check but not since.
---------- Post added January 1st, 2016 at 03:44 PM ----------
If you don't have a local shop anywhere nearby - consider Scubatoys options also. While they don't sell Aqualung they do sell a lot of other well-known brands. And have a very liberal exchange policy - they'll even swap parts on some modular lines like the Zeagle - till you get the right fit. Leisurepro.com also has a personal fit guarantee on a lot of their products. I do not know the details. I also returned a BC to Divers Direct once but they jacked me around for almost two months before issuing the credit.
