external sd - How to recover data from corrupt SD Card formatted as Internal?

My mother has been using the Moto G3 Turbo Edition for almost 2 years now. The device has 16GB of internal memory, but she is using an external Samsung Evo 32GB class 10 memory card as her INTERNAL MEMORY (Thanks to the memory-switching feature of Marshmallow). She has been using the phone with Evo as her internal memory since the phone was first bought. Today while she was using WhatsApp, suddenly she noticed that she was not being able to download any media (music, videos, songs). And when she checked her gallery, she found it empty! Out of nowhere! After further checking it was discovered that the G3 Turbo was not detecting the Samsung Evo at all, eventhough the card was still inside the device. It was showing "No Internal Memory Detected". I tried various solutions like switching off and turning the device back on, cleaning the memory card, clearing cache...nothing works! This has led me to doubt that the problem might be with the SD card. I inserted it into my PC and it wasn't getting detected. The Card has lot of important files in it. What should I do?