Snail mail and insurance questions.

When changing address, you need to bring her documents or mom in person to the post office. My brothers POA did not work until after death and the probate letter indicating I was executor. I brought my mom to both bank and post office when she went to MC. I ensured that her name was primary and the next line had c/o my name. This was important with filing taxes because mom lived across the state line. She had her own state taxes.

You kind of cannot do this half way. If you are POA and paying bills you are not personally responsible for said bills, but you ARE responsible for them being paid. Esp if mom is now in MC. You can't do it halfway. Each entity your mom is involved with will let you know what copies you need to pay and you should be paying out of her account which you sign her name and yours followed by "as POA". NEVER sign anything/not ANYTHING with your name only or you ARE responsible!!!!!

If you don't know how to do this do go to an elder law attorney. They can fill you in.
This is paid for by your POA document and falls under expert advice.
You need a file for each bill and record of when/how paid and copy of check paid with.
You need to call all insurance, including the supplemental insurance. Medicare will be automatic, but other is not.

Again, this is not a choice. You are POA. You can't pick and choose what you will deal with. You are acting for your Mom on ALL OF HER OBLIGATIONS.
Please do see an attorney to be certain how to do all of this. That's crucial. You need to have meticulous records.
Your first year of this is going to be onerous and I know it because I did it, setting everything up. After that it will run smoothly.

There is no renewing of Medicare or supplimental insurance. They continue until you want to make changes.

I suggest you separate Medicare statements from the supplimental statements and put them by date of service. Match them up then match to the bills. Medicare statement will show amount billed, amount Medicare approves and amount actually paid (20% less than approved amt) the balance is then sent on to your suppliment. The balance should be paid by the suppliment if not this is amt the provider will bill. The one way there maybe a balance due the provider is if a deductable has not been met or in my case we have to share the 20%. Providers bill Medicare first, then Medicare sends payment info to the supplimental on file.

Be aware that Medicare sends statements out regularly. They may also send a quarterly one showing everything for that quarter. Put those statements aside, it gets confusing. They are just repeating what they already sent. They do come in handy if you don't have the original statement though. As a POA you are not held personally responsible for her bills. Make sure any checks you sign have POA behind your name. If Mom runs out of money, she has no money to pay bills.