Curious

Not enough pertinent information to offer any real advice.

What type of POA is it and why would you want to change her name?

No matter what the POA says, I don't think any court would approve a name change applied for by the applicant's attorney-in-fact (i.e.: under a POA). So the answer is no.

If there is a valid reason for the change and the wife is totally incapable of making her own decision a court MIGHT grant it, but it's a longshot.

The answer is NO.

The wife will still in most cases have to appear in court and be questioned to reason for name change.

What the others said. And, to add to what I wrote before, many people are confused by the term "power of attorney". It doesn't make you an attorney at law. Only an attorney at law can file pleadings in court, such as name change application for example, for another person such as your wife. Only an attorney at law can appear in the courtroom in behalf of another person. You cannot, POA or not.