Is it a problem if we do not have the I94 during AOS interview?

There could conceivably be difficulty at an adjustment of status interview if the applicant does not have the I-94 card. Although the US government is attempting to abolish the need for I-94 cards in the future, USCIS officers have largely been trained to look for I-94 cards as part of the adjustment of status process. I suggest that your wife file for a replacement I-94 on form I – 102 and show the receipt to the officer at the interview if asked and your wife does not yet have a decision on the I – 102. Due to the limitations of the lawyers.com forums, Alan Lee, Esq.’s (the firm) participation in responding to questions posted herein does not constitute legal advice, nor legal representation of the person or entity posting the question. No attorney/client relationship is or shall be construed to be created hereby. The information provided herein by the firm is general and requires that the poster obtain specific legal advice from an attorney. The poster shall not rely upon the information provided herein as legal advice, nor as the basis for making any decisions of legal consequence.

No.  They probably will not even ask for it.  They have a record of her entry without the need to see her copy of the I-94.