Not sure why you are posting your question in the Scam and Fraud Board but I will try to give you an answer and some direction.
I assume since you have an active/working POA for your parent that they have been declared unable to handle their affairs by their doctor or a court - if that is the case, you are probably handling their SS benefit.
The SSA does not actually recognize a POA for handling SS monies, they ask that you be appointed the Representative Payee or they also appoint someone or institution for incapacitated beneficiaries. If that was not done before then you need to contact the SSA, supply them with a copy of your POA and a doctor or court declaration of incompetence of the beneficiary.
Once you have been appointed as Representative Payee (RP), you can fill out the IRS Form 2848, if needed, as the RP and not involve the incapacitated parent. All this form does is gives you the right to complete or have completed and file their tax return and represent the subject parent for this return. Once you get the RP, you will sign the tax form as such - the subject parent's name followed by your name and the initials of R.P.
You will have to file also with the SSA a RP form also just accounting for SS fund uses.
Here is the Social Security webpage on Representative Payees.
Your problem is that the parent didn't take these actions before she became incapacitated. I understand - had the same problem but as long as you have those backup documents (POA, doctor or court declaration of incapacity) you should have no problem getting the SS Representative Payee status.
Might as well set yourself up as the Medicare Authorized Representative too to save headaches down the road. Talk to Medicare and they will tell you how to apply.
I am going to have the moderator move your post and my reply to the Retirement Board - it will help others there looking for similar info. GOOD LUCK and having been there - may the force be with you. 😉