Maybe a little clarity on shore diving and where you're staying. Comfort Suites is about 50 yards from Seven Mile Beach. What makes it such a nice beach is the flat white sand that extends at least 1/4 to 1/2 mile out in the water. So no reef and no shore diving. Ambassador has an office at Comfort but keeps their boats in a nearby marina and like most operations provide a free van shuttle. Operations like it usually don't have tanks for rental since they're based around their boat operations at the marina.
The only "shore dive" on SMB is Cemetery Beach and it's a better snorkel frankly. No facilities there either - it really is a Cemetery nearby.
So you're midpoint on SMB. For your wife, the Cayman Bus line goes by regularly - she'll be able to easily get downtown or Caymana or the other shopping areas. You could theoretically take the bus to several shore dive locations, it goes right by Turtle Reef and Cobalt Coast (a couple short blocks in) and I believe Lighthouse Pt. also. Just annoying because it is a bus so stops often. If you do ask the driver to tell you when there - it's a residential area and the stop is a block/two away for both.
The best option for finding a buddy is probably Sunset House, most everyone there is a diver or with one. It's not great as a non-dive resort so they tend to attract divers. Afternoons are best since they boat dive mornings as part of their AI resort package. I'm pretty sure I was asked more than once - you can see divers gearing up from My Bar - there's also a spot to the north by the Salt Water Pool so check there also. I'll bet I saw a dozen divers go off the dock or return during lunch.
I've been to Turtle Reef when it was just us for several hours - SunDivers is in the CC building on the waterfront side downstairs. It's pretty convenient since the dive steps are right there but we didn't see anyone hanging around afterward. At that time Macabuca was not there though.
You could possibly find an insta-buddy off a cruise ship at Eden Rock or Devils Grotto downtown but you might wind up being the dive leader. There's maps/websites about both swim-thru's online - once you get to the sandy area stop as further is under the cruise ships and nothing to see.
On those days you plan to shore dive/tour the island, rent a car instead. Andy's has an office on south SMB which is a little closer than the airport, they'll pick you up with a couple hours notice. If you also plan it thru your last day, you can drop the car at the airport on departure, their other office is there. Can't dive anyway so it's what we did.
I'm not really sure you'd find a buddy at Divetech either - you could but it's at a small condo property sort of by itself. They provide a shuttle for their guests from the Holiday Inn on the Sound so should go pretty near Comfort Suites if asked to stop for you. Boat dive with them first to guarantee it. About a 15min van ride - your wife will be bored there quickly - no beach, no anything except Divetech and the small restaurant at the condos.
As good as everybody says Turtle Reef is - and I agree - Sun Divers is mostly a tank/gear rental window and due to both restaurants being on-property it doesn't really promote finding a buddy there. One afternoon mid-week we were the only two there for several hours. Macabuca being on-site now may help that - I could (and would) see going there for a late lunch and a couple dives b4 SunDivers closes. I think Happy Fish Divers is who SunDivers books guides thru - probably with some advance notice.
hth you sort it out.