This means that she will be a US cittizen on May 26.
The ceremony typically shouldn't exceed an hour during which she (along with others being sworn in) will be asked to take the naturalization oath and the pledge of allegiance.
This means, one INS person will read the oath & pledge of allegiance and everyone being sworn in will have to repeat after the INS person.
Before the oath, all people will have to fill in a brief 7 question form (with questions similar to those on N-400), sign the form, turn it in along with the original green card. Example of the 7 questions are: have you travelled outside the country after the interview, have you been arrested after the interview etc.
Then after the oath ceremony, they will receive a naturalization certificate, which has their photo, and which is proof of citizenship.
This original naturalization document will be required proof if you apply for a US passport. Therefore, make multiple copies of it, before handing it to a passport agency (just in case) which will keep it till the passport is processed.
The documents required for the oath ceremony are:
1. Green card
2. Oath letter/apointment
3. Document showing you passed interview
2. Drivers License (proof of identity)
Though not required, it wouldn't hurt to have all the docuemnts carried during the interview-again, just in case.
All the best for the interview.
