Is this phone number a scam

Yes it is a scam. In addition Messenger is a Facebook app that is not affiliated with Apple at all. Make sure she never calls a number on any such message and gives the scammer her Apple Account/Password. If you suspect she has, then you will want to have her change her password. If any financial account details were give, those accounts would have to be secured as well.

Apple would never contact you. Your bank (issuer of card) would contract you. Banks do the exact opposite of the message you received. If they suspect fraud the transaction is stopped immediately. You have to call to verify the transaction, not call to stop the transaction. 

“Don't answer suspicious phone calls or messages claiming to be from Apple. Instead, contact Apple directly through our official support channels.”

”To report a suspicious SMS text message that looks like it's supposed to be from Apple, take a screenshot of the message and email the screenshot to reportphishing@apple.com.”

You can report phishing at these links and most importantly your local law enforcement.

• Identify legitimate emails from the App Store or iTunes Store.
• FTC Complaint Assistant
• FBI’s Internet Crime Complaint Center

Learn about how not to be a victim of Social Engineering.

Recognize and avoid social engineering schemes including phishing messages, phony support calls, and other scams - Apple Support