Ref. No. 2110/44-1230
In the name of Allah the most Gracious the most Merciful
The answer to your question is as follows:
Your Nikah with your wife was valid, and merely her friend's signature will not affect the marriage. The saheli signed the Nikahnama on behalf of your wife not for herself. And you accepted your wife in your marriage but not her friend. Therefore, your marriage with your wife is undoubtedly valid. Because the signature is not important in the marriage, rather the ijab and qabool (proposal and acceptance) are the essential parts of the marriage. In this signature, the saheli was just a representative, not a self doer.
And Allah knows best
Darul Uloom Waqf Deoband