Hola, and welcome to The Cabe Gaston.
Nice find and it looks to be in good condition for its age.
I think this Armstrong could be from the 1930's or 1940's, as I don't believe Armstrong made a ladies loop-frame design in the 1950's. It's certainly not shown in their 1951 catalogue.
Here is an image from the 1936 catalogue, showing the two loop-frame models available.....
...I think yours may be the top shown example as the lower version is a 3-speed model.
It looks like you may be only missing the enclosed chainguard.
The 1936 catalogue cover also shows the same design for "Armstrong" that appears on your handlebars.....
...a loop-frame model was still available in the 1939/40 catalogue.....
...but possibly loop-frames weren't available postwar.
Here's the image of the logo from 1939/40.....
As to your saddle, it's a "mattress" type, possibly made by Brooks, Terry's, or possibly another manufacturer. The catalogue descriptions (above) unfortunately don't name a manufacturer.
Several companies offered this style of saddle at the time.
Here's an image of Brooks 'mattress' offerings from 1935, this should give you an idea of what you're looking for.....
...I hope this helps, good luck with the project!