Bluher popped the question at the resort Thursday evening while the couple relaxed on the beach beneath a white tent filled with white roses and lilies, Us Weekly reported Saturday.
Bluher presented Armstrong with a gold and diamond engagement ring designed by Ari Soffer. The couple had a lavish dinner afterward at the resort's restaurant, Carolina.
"The St. Regis Punta Mita Resort is where we fell in love, it was the perfect choice for this wonderful occasion," Bluher told Us. "Taylor was beautiful and never stopped smiling! it was an amazing evening, a ten all round!"
The pair hasn't announced a wedding date.
Armstrong was previously married to Russell Armstrong, who committed suicide in August 2011. She shared a daughter with him, Kennedy, 6.