Credentials constantly asked when opening office files on SharePoint

One of our customers have an issue with her SharePoint Office 365’s files.
When she want to open it, her credentials are constantly asked.
We had the issue on the mapped Network-attached drive and on IE but after several searches on the net, we found how to solve the problem on IE. But there’s still the problem for the Network-attached drive (Which is the same SharePoint folder but accessed by the Win10 Network’s menu).

Her credentials are right, she can access to the documents from the Network-attached drive but she must type her credentials every time she wants to open an Office Doc.

We’ve checked that her credentials were correctly registered in her windows account and that the PC is correctly attached to the domain.

Does someone have a clue or know what we have to test/do to solve this issue ?

Thanks for your attention.

Best regards.