Should I tell my friend the truth and take the risk?

I have a friend. Let’s just call her Lilly. We work together. She’s a really enthusiastic and nice person. When I needed help she was the first one to help me. When my car broke down she offered to drive me back and forth to work for a couple weeks until it got fixed. When I was short a money she gave me money and didn’t ask for it back. When I have to vent, she actually takes the time to listen to me (most people don’t). I was happy for her. She worked very hard for this job and finally got after years of hard work. Unfortunately, I had a discussion with our boss. He told me that he didn’t think that Lilly is performing well on the job. He told me that in a week he’s going to terminate Lilly from her position. The boss told me not tell anyone this information, especially Lilly. I feel so bad seeing Lilly smile everyday knowing her fate. I feel really wrong talking about the job and smiling in her face knowing she’s going to be unexpectedly fired. I really want to warn her, but if she finds out word will get out. The boss would know that I told her and we’d both get fired. Lilly has done so much for me. Should I take the risk and let her know about the termination?