Another practical route for you to pursue is with your bank on the basis you only authorised £9.95 to leave your account and not £59.95, so an explanation needs to be given as to how your bank let the full £59.95 be debited.
However, I would say the strongest legal argument arises from the transaction when the gift card was bought by your sister.
She paid for goods, namely in this case a gift card to the value of £50. However, through no fault of her or you, the goods bought are not – to quote the relevant words in the Consumer Rights Act 2015 – “fit for purpose” nor indeed “as described”.
In law, “fit for purpose” means the goods should do what it is claimed they should do. In this case, the gift card bought by your sister very clearly is not working as intended because you cannot use it as a gift card.
Your sister therefore needs to contact the company and ask for a full refund, saying if it doesn’t refund her within, say, seven days, she will issue a claim in the Small Claims Court (you can see how to do this on gov.uk).
Or, if your sister used a debit card, she could ask her bank to invoke the so-called “chargeback” procedure to be refunded on the basis she used the card for goods which have not been provided.
There is no limit for chargeback, whereas for the equivalent procedure for credit cards as per Section 75 of the Consumer Credit Act 1974 the disputed transaction must be between £100 and £30,000.
Once your sister has been refunded, you and her can decide if you want to re-engage with the company and re-order or not. I guess that decision will be influenced by how it deals with you cancelling your order and returning any items already sent to you.
If I was a senior person at the cosmetic company, I would also be reaching out to you and your sister to apologise and offering to send you a goodwill gesture of some kind. That is not the law, it’s just good customer service and common sense if they want to keep you as potential customers.
Ask a Lawyer should not be taken as formal legal advice, but rather as a starting point for readers to undertake their own further research.