What is the best way to enable my sister to make purchases for my elderly mother?

Why don't you as POA apply for a CC for your mom. The credit limit can be set low and the monthly statements would come to you so you can keep track of things.

I got a credit card in my own name and used it exclusively for my mother's expenses. I paid for it out of her bank account as I was her POA.

A tip if you do this -- Find out if the nursing home accepts credit card payments for the monthly bill. The first nursing home my mother was in did accept them, and we got about $250 a month back after paying off the bill each month.

If that's the case for your mom's place, make sure you get a credit card with a cash back feature. I got a Citi Mastercard and I know Discover is a cash back card as well. (Some places still don't take Discover, though, so check in advance.)

I make all the purchases for my mom using her debit card. I’m 4 hrs away.

My Mom has her savings and SS check feed a checking account with a set amount of money each month, which pays her bills.
We have a credit card in Mom's name linked to the checking account. I purchase things for my mother with the credit card, the POA goes online and approves the credit card payment each month. For big purchase items I take a picture of each receipt with my phone, and send it to the POA, or if it's an online purchase I email him the receipt.

Give your sister your credit card or make her an authorized user on your CC acct with a card of her own. All charges will go to you.

Another way is to set up an account for your sister with said amount in it to use for your mother. Then this account with you on it too will have money in it with a debit card attached to it. You will be covering both your butts then if anything comes back to say where is the money spent.

Prayers

There is also credit/debit card called True link which helps track all spending, which enables you as POA, to carry out your responsibilities but let’s your sister do what is needed. You can get it in your mother’s name but give it to your sister. It gets linked to your Mom’s checking or savings account, you decide. There is a monthly fee but for me it is worth it since you can get reports as POA, you can also limit where purchases can be made etc.

Billing should go directly to you for any purchases. This can often be arranged through credit card that is for your Mom's accounts specifically, or debit card. Speak to the banker where you maintain your mother's accounts. As POA you are responsible for a PAPER trail that accounts for all purchases made for your mother, every penny in and out of her accounts. Speak to the banking manager where you do your POA work. Or speak with an accountant.

Your Sister can send you receipts, also, on a monthly basis, for which you can create your files and write out a month reimbursement check to her, keeping all of this carefully accountable by saving receipts and keeping copies monthly of her presentation of receipts and your check outgoing.

Good luck. Hope you find what works best for you. POA is no easy job; I did it for my brother as well as acting as his trustee. We lived in same state and not the same town and it was complicated, to say the least.

my daughter has a credit card issued under our account in her name. Check with credit card company if that can be done.,We gave her the credit card when she was in college. We decided to continue it even now because it is convenient for her to have it if she is helping us out with something. We trust her 100% and she certainly does not abuse the privilege.

Debit card. Similar situation/distance here. My sister had the debit card, let me know when she used it and I entered it in checkbook. Rarely, she'd forget but it showed up when I reconciled account.