Our living room is 33 M2, and an adjoining mancave of 9 m2, a total of 42 M3. The main living room has an 18,000 BTU unit (Samsung) while the mancave has a separate 9,000 BTU unit (Haier). Both are the newer Inverter technology, both work well. All the air conditioners in our house, 4 of them, are serviced and cleaned twice a year, the air filters are cleaned by myself every month or so.
For your room, I would be inclined to have 2 x 13,000 BTU units, inverter technology. Why? Four reasons: firstly, 2 air conditioners would provide built-in redundancy should one fail and need maintenance, secondly, 2 x 13,000 BTU units are about the same price as 1 x 24,000 BTU unit, thirdly, 2 units evenly spaced will help to circulate the air more evenly around the room and, finally, for much of the year, 1 x 24,000 BTU unit would be overkill. As with our living room/mancave, one unit and a fan will often provide the optimum cooling effect. During the very hot weather, both units are required, but during the cooler season, one or the other is usually enough. Your large glass-fronted wall is north facing and should not adversely affect your air conditioning requirements too much.
As
@Rice has mentioned before, the internal workings of the air conditioners of different manufacturers use many common parts. Therefore, when it comes to choosing one particular make from another, there may be little to choose between them. We have known our air conditioning engineer for maybe 15 years, he has a successful business installing thousands of units a year, and is a likable chap too. He usually comes around to service our machines within 24 hours of receiving a call. He can offer professional advice, recommend the best buy for you, then buy and install said units. If you would like his number please drop me a P.M. Alternatively, I would recommend HomePro to buy and install.
Install a curtain rod and have her make curtains over the window. You will be amazed on how much ac you do not need.