samjuno: she purchased $5k and listed me as a "Co-owner".
There will be no problem as the limit is based upon 5K per SSN. Since she used her SSN, and not yours, her purchase will not count towards your 5K limit.
No need to change the registration. Indeed, in the present registration, if you can get your hands on the bonds, you can cash them yourself and run off to Fiji for a nice vacation. :-).
Dick