That being said, I also bought a used (tested, cleaned, certified, and rated) lens that I thought was 25-85mm f/2 but it is f/3.5-4.0.
You can find f/2.8 zooms... but that's about as low as they go. Lower focal ratios are generally only available in "prime" (non zoom) lenses. I say "generally" because there's no reason why it's not possible... but it's difficult to design and get good image quality and the costs become ludicrous (as if f/2.8 zooms aren't already expensive.)
Also, let's say I took her image of my son (which I won't!) and sliced the unfocused portion into another layer in photoshop, and just sharpened that layer. Would that be another workaround?
There are limits to what you can do with sharpening.
See this article:
LensRentals.com - Have You Seen My Acutance?
Specifically see "Figure 1" and "Figure 2" in that article. Each has 5 blocks of vertical stripes to some varying degree of "sharpness".
Look at Figure 2. The 5 vertical stripe patterns are as follows.
1 - block 1 is in sharp focus.
2 - block 2 is slightly soft -- just a little.
3 - block 3 is very soft.
4 - block 4 is REALLY block 2... after applying 'sharpening'
5 - block 5 is REALLY block 3... after applying 'sharpening'
And here's the take-away. Notice that block 4 (the 'sharpened' result of a moderately out-of-focus area) can be cleaned up, but block 5 (the 'sharpened result of a very out-of-focus pattern) cannot be cleaned up? This is because the software needs to be able to distinctly recognize what it's trying to clean up and there needs to be space (gaps) between each "stripe" in the pattern.
When the details are there... but slightly soft... you can clean them up. When the image is so blurry that the details aren't there anymore (they all start to blend together because the blur is strong) then sharpening software isn't going to save you.
Also of interest... go back to Figure 1. This is the same as Figure 2 except the stripes are larger, bolder, and have more spacing between them. Because of this, it WAS possible to sharpen both the 2nd and 3rd set of stripes. But look CLOSELY at the results. Notice that the "sharpened" results of the stripes widen at the top and bottom? ...and yet looking at the first image in the row -- which is the "in focus" version -- these stripes are perfectly parallel and consistent width from top to bottom. This is an artifact of the sharpening process. When sharpening is applied, it's never quite as good as an image which needs no sharpening.
However... with a narrow depth of field, it is possible to take lots of images ... each focused at a slightly different distance... and then merge them together. Image stacking will allow this and Photoshop will do this. It's a problem when doing close-up photography so it's a fairly common technique among macro photographers.