Well, there's a couple of different ways to go with this.
You *could* try slowly moving her to 1 nap. She's definitely old enough -- avg is 15 months for 1 nap -- but every child is diff, and she may be one of those slow transitioners! If she *is* a slow transitioner, then forcing her to 1 nap will only bring on OT hell.
The second option is to simply wait to MDO for a month or two and wait for her to transition to 1 nap on her on.
The plan for transitioning her to 1 nap would be to move AM nap a bit later at home She's only doing 2-2.5 hours A time right now, which is really really short (6 month olds can do that!). Let's try a 10:30 nap for 30 minutes on Days 1 and 2 and then do a PM nap from 2-4 then bedtime at 7:30.
Then:
Days 3-4: 10:45 nap for 30 min; PM nap 2:15-4:15; bedtime 7:45
Days 5-6: 11 nap for 30 min; PM nap 2:30-4:30; bedtime 8:00
Days 7-8: 11:15 nap for 20 min; PM nap 2:30-4:30; Bedtime 8:00
Days 9-10 : 11:30 nap for 20 min; PM nap 2:45-4:45; Bedtime 8:00
Days 11-12: 11:45 nap and let her sleep as long as she wants (this is us moving to 1 nap!); hopefully wakes 1:45 and then bedtime at 6:00
Days 13-14: 12:00 nap for as long as she wants (hopefully 2 hours); bedtime 6:30.
Now, as you try this you may see things really start to get bad. If that's the case, it means she just isn't ready yet. At that point I would back up to the 10:30 nap for 30 min routine, and then keep her there for several days before trying again.
Most kids have transitioned to 1 nap by 18 months, so at most you probably have 6 weeks before she's on 1 nap. However, even when she *does* make it to 1 nap, there's no telling if she'll be able to handle the 12:30-1 nap time that MDO has. If it were me? I'd wait another month before doing the MDO thing. It could save you TONS of NWs and EWs and grumpy kid problems! It's only another month, but to me it would be worth saving the heartache at home trying to move her into a sleeping routine she's simply not ready for. She must be a sleepy kid indeed to still be doing 3 hours of daytime sleep at 16.5 months. That may mean that she just won't be able to stretch to a post-lunch nap for awhile yet.
The good news? I also have a sleepy kid! And we couldn't do activities like the one you describe until post-18 months either. However, my son will be 4 years old in a month and he still takes 2-3 hour naps and sleeps 12 hours at night while most kids have already dropped their nap. So count your blessings! Sleepy kids can be diff. early on b/c they limit your ability to get out and about, but in the long run their will be more 'you' time, so celebrate the child you have!