Dual Citizenship Notification

Hi,

I had a quick question regarding dual citizenship with UK and Russia, basically, my wife is Russian and become a British Citizen last year, does anyone know if she needs to notify Russia that she is now a dual citizen?

She’s been living in the UK for 8 years now and hasn’t returned to Russia since living in the UK, she’s received an official letter in Russia and unable for any of her family members to retrieve the letter, obviously a slight panic but just wanted to see if anyone has experienced this or knows the rules