You may want to check that you are sending the notice of your US citizenship to the right place. Where you should send your notice depends on how far along your I-130 petition has gotten.
If your petition was approved, the file generally would have been sent to the National Visa Center, an office of the State Department and separate from USCIS. You can review the information provided by NVC to see where you should send your notice of acquiring US citizenship. The website for NVC is http://travel.state.gov/visa/immigrants/types/types_1309.html .
If USCIS has not approved your petition, USCIS would be the place to send the notice of acquiring US citizenship.
If after a month you do not hear back from the office where you send your notice, you should start checking whether your notice has been received.
Also be aware that foreign national who are married to U.S. citizens can apply for legal permanent residency without waiting for the I-130 to be approved.
To get professional advice as to whether your spouse should apply with adjustment of status or consular processing, and the risks (if any) of both processes, please call my office and schedule a consultation.
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After notification of the USCIS of your change of status, the approval should normally take about 3-4 months (based on current processing times) since this is the processing time for a case initially filed for the spouse of a US Citizen. Ironically, the USCIS may take longer to change the category of the visa then it would to process a new US Citizen-based petition in some cases. However, you may be able to push the case through faster if your wife is eligible for adjustment of status. If so, then she can file the adjustment of status case with the proof of the change in petitioner's status and a copy of the receipt notice for the pending case to get the case on the Immediate Relative track. My clients are receiving interviews in less than 3 months in some cases.
Best of luck.