I want to know the answer to the following question:
Which singer did she join on MTV Unplugged to sing?
All the background I'm provided with is that "She appeared at the 56th Annual Grammy Awards in January 2014, performing "Open Your Heart" alongside rappers Macklemore & Ryan Lewis and singer Mary Lambert, who sang their single "Same Love", as 33 couples were wed onstage, officiated by Queen Latifah.". Is that enough to answer the question?