Unauthorized user changed my password and email

HI!

i am writing on behalf of my client. She owns the company Soul Kiss FIlms and the domain https://www.SoulKissFIlms.com. It appears that someone has gone into the backend of her wordpress site and changed the username and/or password and the corresponding email associated with the account. Changes have been made to the site by another unauthorized party, and we no longer have access to her site.

I have been hired by Ms. Bader to work on her site and marketing. I have her emails and previous login information for reference, if needed.

Ms. Bader needs to have access to her site and it has been compromised.

Please advise me what to do on her behalf.