So, I'm new on these forums.... can you give me a link to a good example of N-400 process could be aggravating? After all the work involved with getting Green Cards, the N-400 process seems pretty straight forward. Am I missing something?
For most people it is straightforward ... file the forms, give the fingerprints, do the interview, take the oath.
For some people however, they get a hostile interviewer who asks tons of questions and demands extra documents to be produced which the applicant doesn't have on hand. Then the applicant later sends in the documents a few days later, but doesn't hear anything from USCIS for months and months. Then ultimately it takes a year or more of waiting, including the applicant filing a lawsuit, before USCIS finally decides the case.
For others, they have an extensive travel history outside the US, and are denied citizenship because of failing the continuous residence or physical presence requirement. Then they have to wait 4-5 years to apply again. But if your case is approved before your child is 18, your child's travel history won't matter; she'll become a citizen automatically on the same day you take the oath, and then you can go and directly apply for a US passport for her. Optionally (preferably after obtaining her passport) you can file N-600 to obtain a certificate of citizenship for her, or advise her to file it on her own when she's 18. It is not a necessary document, but unlike the passport, the certificate doesn't expire so it may be useful in the future if the passport is lost or expired and she needs to prove her citizenship.
Given that you can apply 90 days before the 5-year anniversary, it is very likely that you or your husband's citizenship will be approved before she turns 18. But don't apply exactly 90 days before; wait a few days extra because USCIS is known to miscount the days and wrongly reject applications that were filed exactly on the 90th day (sure you can appeal or reapply, but that it itself wastes weeks or months of time). Make sure the signing date and the postmark are both a few days after the 90-day cutoff, to protect yourself from their mistakes.