First of all, cancel your Credit Card immediately.  Explain the situation to the institution & provide them a list of all fraudulant transactions. They should restore (credit) your mum's account within a week or so while they investigate the situation.

Just 3 weeks ago my credit/debit card was hacked into WHILE the card was in my posession!!        I learned that anyone with a "card reader" can simply stand by your side as the card reader retrieves your CCard information from your wallet or purse.  More specifically I understand that using your CCard at the gas pump, rather than paying inside the sation, is the most common area for hackers to retrieve your CCard information. Anywhere you use your CCard which requests your 5-digit zip code is at higher risk of hackers to obtain your information. 

Good Luck to you & your mum. Cheers!