Thanks! I didn’ see this in time, so deleted the app and files on the 2nd iPad. The original (VERY small, since I’ve just started using Obsidian on the first iPad), is fine.
It turns out that my original vault is not on iCloud, which certainly explains why iPad 2 isn’t seeing it! I remember seeing that the location could not be changed, so I don’t know what happened or what to do now.
Would it work to make a copy of the vault files somewhere, then delete the originals, create a new vault from iPad 1–but in iCloud—and then move the saved files into it? Since I’ve just started using Obsidian, there are very few files at this time…