When I posted one of these individuals a bit ago, you told me specific views I would need for a species level ID. Those are shown in the shots here-- is it still not possible? I put a lot of effort into getting these photos, going so far as starting my own research project in my 2nd week of Uni, so I would really like to get a species here, even if it means describing a new one.

the pictures are not good enough to do even an attempt of a species identification. For example, the shape of the winged teeth of the unguis should be distinctly more visible. The winged teeth are different in each species. Note also that the winged teeth are asymmetric. So it is required to see the difference in the winged teeth (left and right).
Also the chaetotaxy of the labrum and labium should be made visible.
If you require a species level ID, pls follow the key at www.collembola.org to find out what characters you have to make visible in the pictures.

It sounds a lot like I'd need an electron microscope for this, which is not something I can get access to. Is it possible for me to just send you some samples of this species? I have been trying my best to do this, but it is getting too complicated for me to follow. Also, what is the likelihood of this already being a described species? I haven't found any records of Pseudosinella
species in the PNW.

an electron microscope to see these features. An optical one will do fine. But you need to clear your specimens. Such as in lactic acid. Once they are cleared properly you can transfer them in ethanol to observe the features under the microscope. No need to send me samples. Most probably it is a described species. Pls clarify 'PNW'.

If I need to clear them in lactic acid, how long do they need to be in it, and at what concentration?

"PNW" is an abbreviation of "Pacific Northwest" (The states of Washington, Idaho, Oregon, as well as Northern California and British Columbia in Canada).

Lactic acid 10% will do fine. You can soak the specimens for at least a day at room temperature. The clearing will start immediately, so you could follow the process under the microscope. The purpose is to 'remove' all the soft tissue. The remaining chitin structures will become better visible (less obfuscation).