Help needed with sentence analysis.

Posted for a friend of mine who is pulling her hair out! Can anyone help?

Q: "2 Lea House is a beautiful Victorian Mews property believed to date from 1890."

Is that a Simple sentence and noun phrase OR insert ‘which is’ (conjunction/prepositional noun?) to make complex sentence with independent and dependent/subordinate clause?

Also is the head 2 Lea House or the Victorian Mews?

Thank you.

"2 Lea House is / property

Victorian Mews = adjective

believed to date from 1890 = adjective clause