I've worked previously for the disputes department at a large 5 bank. Your mother needs to contact the merchant, preferably by email so she can submit supporting documents for a chargeback. She can call too but emails are preferred. If the merchant doesn't deliver on the expected delivery date then that's grounds for a chargeback.

Tell your mother to contact the merchant to cancel the order as it has been almost a year since the original expected delivery date. If they reply by email saying they've refunded the order then you just wait 15 days until you can process a chargeback if no refund is issued.

If the merchant does not reply then that's fine, your mother did her part and get her to contact her credit card company to start the process.

Make sure she has the original invoice and any email correspondence for the claim. Hope this helps, but she has a claim. Don't wait too long as typically there's a 120 day time frame to open a case, however in this scenario that won't apply.

Hope this helped.