Unable to erase SSD

The SSD will have to be reformatted to become usable. Since you can access the SSD, I suggest you backup your data. When that is finished, use Disk Utility to erase the SSD. You can then install macOS from scratch using Network Recovery.

Internet/Network Recovery of El Capitan or Later on a Clean Disk

     If possible, back up your files before proceeding.

1. Restart the computer. Immediately, at or before the chime, hold down the (Command-Option-R) keys until a globe appears.
2. The Utility Menu will appear in from 5-20 minutes. Be patient.
3. Select Disk Utility and click on the Continue button.
4. When Disk Utility loads select the target drive (out-dented entry w/type and size) from the side list.
5. Click on the Erase button in Disk Utility's toolbar. A panel will drop down.
6. Set the partition scheme to GUID.
7. Set the Format type to APFS (SSDs, only if installing Mojave or Catalina ) or Mac OS Extended, (Journaled.)
8. Provide a volume name, usually "Macintosh HD."
9. Click on the Apply button, then click on the Done button when it activates.
10. Quit Disk Utility and return to the Utility Menu.
11. Select Install OS X and click on the Continue button.

Jseegs Said:

"Unable to erase SSD: [...]My next step is trying to install using a USB installer (but don't currently have a USB drive large enough)[...]"

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Use a USB Flash Drive that is 16GB.

Trying the USB Bottle Installer is way to go from here. - Do you have one laying about? If not, just get one at your local retailer.

For Note: 8GB are tough to come by as individual packs, as they are now becoming more, and more, obsolete. So, you'd probably only find an 8GB USB Flash Drive in a multipack.