I'm Doug, and I'm sorry to hear of the confusion. My goal is to provide you with excellent service today.
Pursuant to the terms of your obligation as agent under your wife's POA, you are obligated to keep her funds separate from yours. And because funds in a joint account legally belong to each of the co-owners of that account, it would be a violation of your duties as agent to deposit these funds in the joint account.
You can certainly ask her permission to deposit those funds in the joint account, and do long as she is competent and can sign her name on a paper you prepare giving you authority to deposit to the joint account, then you may do so.
Otherwise you will need to open a new account in her name with you as trustee of that account and deposit the funds into this new account.
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I wish you and yours the best in 2015,