Yeap, it arrived yesterday and it is for Dec 18 @San Francisco office, the bad thing is that my wife had to leave the country due a family emergency and will be back the 1st week of January, so the only option is to reschedule, will see how far back it will put her application.

i rescheduled my fingerprints for Removal of conditions for 8 months and still got approved, so nothing wrong with rescheduling itself

as to delay, i think (my private opinion, i may be wrong) that this 2 processes are completely separate timelines

1) fingerprints and FBI clearance (Name Check etc) that in some rare cases can last years after the interview and sometimes requires a lawsuit against USCIS to finish it, and they cant give you oath date until you are clear

2) application mailed-> NOA1 >- waaaaaiting time (about 6-8 months, but now they say 16-18) and then your turn comes and ->you get interviewed and then if FBI didnt clear USCIS waits for it to complete, once it's done -> you get oath date.

so i personally think that fingerprint reschedule don't delay your interview, but may delay the oath, cus it's 2 different processes probably handled in separate departments.