You only get BAH if you are living off base. Since you are in schooling you probably are living in the barracks so you are not entitled to BAH. If you want it at the WITH DEPENDENT rate you need to have a dependent and you have to enroll them to get them on record.
As far as a power of attorney, you do not need a lawyer to do that. Look up SPECIAL POWER OF ATTORNEY on the internet and make one up. All you need is a couple of witnesses to verify your signature and perhaps a notary. It would go something like this.
SPECIAL POWER OF ATTORNEY.
I, John Doe (334-33-4455) serving in the US Army do hereby grant to my wife Shelly Doe (333-44-3333) a special power of attorney for the sole purpose of going onto a military installation, into a federal office or other agency that can enroll her in DEERS for that purpose.
She has been informed she needs two forms of photo ID, a certified copy of our marriage license, a certified copy of her birth certificate and a copy of my orders to active duty. This special power of attorney is effective from the date signed below to 90 days after that date.
________________
John Doe 22 March 2013
Witnessed: ___________________________
Peter Shelly (44--33-2324)
Witnessed: _____________________________
John Burk (222-33-2329
I John Doe, do hereby affix my signature again to this document for the purpose of Notary ID.
__________________________
John Doe
Notary in the State of Colorado.
The above signatory identified to me by valid photo ID..... (The notary will supply this info you do not have to type it. You need to sign the last signature in the presence of the notary and he/she will
notarize the document.