My girlfriend is getting certified and I want to take her on a trip somewhere so she falls in love with diving. I'm fairly advanced and looking for something that will be easy for her (shallow reef, minimal current) but still be engaging.
It's a good question, with more than one potential answer. I'll post some resource links, but start with some thoughts on various places already mentioned.
1.) Key Largo (upper Florida Keys) - shallow reef diving over flat bottom, pretty nice corals, fishier than some other places, some medium/large creatures, viz. maybe 50 feet so not up there with the Caymans or Cozumel but good enough, and it's U.S. so money, language, laws...pretty much what she's used to. But don't expect nice sandy beaches sloping into the ocean for wading. I was there once, in 2013. Others mentioned seas can get rough, and boat rides aren't real short; consider time of year you plan this trip and ask how seas tend to be then.
2.) Bonaire - great for packing in shore dives, but that means changing tanks and gearing up on the tailgate of a pickup truck. Limited topside. Love Bonaire, but at this point...not what I'd recommend, especially if you've never been and aren't comfortable driving around it yet. Not a sandy beach destination.
3.) Curacao - more happening topside than Bonaire, people seem to mix shore and boat diving more than just shore diving only trips, and you get sandy beaches. But...for a first time newbie, I wonder if staying closer to Willemstad rather than the rustic Westpunt might be a better choice? I've been to Curacao once - staying at Sunscapes Resort Curacao (an A.I.; since then, there are now 2 more A.I. places, I'm told).
4.) Roatan - Just got back from CocoView Dive Resort; really liked it! But if a sandy beach is a big deal, you'd pick a different place than CCV. Be mindful of the biting 'noseeums' and the need to use bug repellent.
5.) St. Croix - loved our trip, but not convinced the diving is quite on par with some other places. Topside is a varied, engaging island...but in a somewhat subdued way. Not a 'water park, roller coaster, zip line, paid dolphin interaction' kind of place. Sandy beaches.
6.) St. Thomas - 2 training dives, 2 'regular' dives there. Sandy beaches, popular cruise port so plenty to do topside (including shopping), what I saw entailed shallow diving over hard bottom, good viz. but not on part with Cozumel or the Caymans, wasn't as fishy as Key Largo. Jaan Leemet made a post that may come in handy -
Thanks Steve and I'm sure you'll enjoy it. Tell the folks at Aqua Action hi from the Jaan and Nat, the DRYFOB folks

In case anyone else is interested in reading Nathalie's write-up I've also included a link here:
Scuba Diving Vacation at Secret Harbour Beach Resort in St. Thomas, US Virgin Islands | Freedom Tour Travel
7.) Ambergris Caye, Belize might work. I've only dove Belize via live-aboard.
Loved Cozumel, but it's drift diving in current, and not everyone readily takes to or likes that. Turks & Caicos tends to be deeper diving, and land-based has a rep. for long boat rides and Provo. is expensive. Not recommended for a newbie aiming for shallow diving. Too bad Grand Cayman's not open right now.
Key Largo with Rainbow Reef Dive Center 2013 -
http://www.scubaboard.com/forums/fl...iving-key-largo-rainbow-reef-dive-center.html
St. Croix Research Report Aug. 2017 -
Trip Report - St. Croix Research Report Aug. 2017
Turks & Caicos Research Notes -
Turks & Caicos Research Notes
My Research Notes from Planning Cozumel Trip -
My Research Notes from Planning Cozumel Trip
Curacao Trip Research Notes
Curacao Trip Report with SB Surge Jan. 2019
My Research Notes for Bonaire -
My Research Note For Bonaire
CocoView Trip Report May 2021 -
Trip Report - CocoView Resort May 8-15, 2021
My Research Notes from planning a Roatan Trip -
My Research Notes from Planning Roatan Trip
Out of all that, my short list would probably be Key Largo, Roatan (some places), Curacao or Ambergris Caye, Belize. If your trip will be in peaks times of 'hurricane season,' Curacao sounds really good (the ABC islands miss most of the hurricane and tropical storm drama).