Hello, and welcome!
What type of safe is it/who is the manufacturer and what is the model number?
If it is made by Sentry, the only way to open with the key is to order a replacement key from the manufacturer. You can do that at the website below. Just follow all instructions and be prepared to download and fill out a notary form, confirming safe ownership. CLICK HERE
as you can see, you can request 'expedited service and get the key within 2 business days (unfortunately, they are closed on the weekend, so you would have to wait until Monday or Tuesday, due to the holiday, to have your order processed.
If your safe is made by another manufacturer, please let me know and I will be glad to help you further.
If this is an emergency situation and the safe must be opened immediately, you can call a locksmith or safe technician in your area and have them open it for you. Depending on the type of safe, they might be able to open it without rendering it unusable or they might have to drill it open.
While this may not be the type of answer you were looking for, it's the only alternative, so please take that into consideration when rating. Thank you!
Please be so kind as to rate my answer with positive feedback so I receive credit for my assistance. Thank you.Rating will not cut off our communication and you can click 'Reply' to ask for any clarification or additional information.Warmest regards,Cher
I wish you much good luck with your mother's safe!