Ariel's recommendation is 5'7". It might fit her if you got rid of the suspension seatpost and used a rigid one, but there is no guarantee of that. Also, the handlebars would be very high relative to the saddle. She might enjoy that, but if not, then a different stem would be in order.
I there a particular reason you want to get her that specific model?
What features specifically? If you are looking for a class 2 mid-drive, that would narrow the field down considerably, especially if you are trying to keep it around the same price point. The only bike remotely close that I can find is the Espin Reine at $2K, and that is currently unavailable, and it does not have an IGH system nor a 48V drive.
The Giant Momentum Vida E+ is a step-thru with a mid-motor and IGH, but no throttle, no suspension, and no 48V. Plus it is considerably more (partly due to it being from a "real" bike company). It would definitely fit though in the small size.
Slightly off-topic, it amuses me that in some of the Class C photos the seatposts are installed backwards.
Even we are thinking about buying Ariel M class for my wife who's 5ft. So which review were you referring to? Is there a new review for newer model.? The review on ebr is 2 years old.
The review is on Ariel's site under M Class.
You might also want to look at the Aventon Pace 500 in size small, but I think I like the Ariel a little better.
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NOTE - The new Ariel M Class is significantly better than the 2018 model reviewed on this site.
There seems to be some problems with Ariel Rider Customer Service, you might want to check some of the comments here on the forum for the M-class. I did try out the Aventon Pace 500 and it was my 2nd choice, I went with the Giant LaFree E2, but it costs a little bit more.
I'm not sure how you came up with that 1/2" difference in seat height because the dimensions at the Ariel Rider website look very sketchy to me. There is a review on page 3 on the Ariel site for the C-Class where a woman a bit over 5'4" said the bike was much too tall for her. So far as I know, the dimensions should still be the same now as from the version in her review. I'd suggest you call Ariel to clarify the difference between the Class C and M bikes.
If you want a mid-drive bike in a similar price range, you might also consider a Motobecane such as this one (however delivery is not until Sept):
That bike offers a size small step through frame for 5' riders. The components are mostly Shimano which should mean good quality and reliability.
They also have a lower cost step through available now, but the stated minimum height is 5'3":
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I think the Aventon bikes look solid though I've read they take a bit more effort to assemble and they don't have a mid-drive. You can get them assembled from a local dealer (same price as the website) if you have one near by. If I got an Aventon, I'd go for the Level model which does offer a small frame but the stated minimum height is 5'1". The Pace 350 or 500 should be fine too if you don't need the front shock or fenders.
There is a Facebook page for Ariel Rider owners which you might take a look at as well. It might take a few hours to get approved to join it.
N95 mask should work, but I've stopped biking as the average for the last week in Salem, Oregon of 406 AQI is just too much.It seems the 2020 C class is a little different from the one reviewed on ebr. The minor, but annoying problem I've encountered is that the downloadable manual has info on the display that doesn't quite fit the actual display. Different buttons, for example, located differently. Haven't had the opportunity to put a lot of miles on it, and don't really know how many miles that is. That's because the speedo and odometer weren't working. I finally resolved that (magnet on spoke was aimed the wrong direction so the pickup sensor wasn't reading it). And now we've got this wildfire smoke drifting in from eastern Washington and Oregon, making outdoor activities problematic. We need coronavirus masks that also filter out smoke, but I'm not aware of any that do.