A life cut to short

I just learned that an acquaintance of mine just lost her battle with cancer. She fought hard for
3 1/2 yrs. Shauna was only 41, had a husband and two kids. Why did God take her from her family?
She wanted so much to LIVE, she loved her family, friends and life so much. Does not seem fair.
I met Shauna online through a local scrapbooking group that I belong to, back in 2002. I did not know her that well but from what I have heard, she was an amazing person.
Here is a link to her blog...http://shaunaimmel.blogspot.com/
Her last post was just days ago. I cried while reading her thoughts, so grap a tissue. Even though you may not know her, I think you'll be touched. I kept putting myself in her shoes and what I would be thinking if I were her. Of course my kids and not seeing they grow up, Christmas and other holidays. My daughters first boy friend, wedding, babies.........
what Cory would be like all grown up, his wife, babies.........oh my, it was just too much for me to think about.
Now on top of all this, my bunco friend, who is Shauna's good friend, is having health issues and the nasty 'C' word was brought up by her doctors. She's scared, I can't blame her after watching her friend fight and lose.
So, now I ask.........do I pray for her to be healed, do I pray for God's will, or do I not pray at all, because God already has his mind made up? I just don't understand this part of prayer.
I do pray, the bible says to pray. I know my prayers have been answered in the past but why are some answered and some not. Ya, ya, I know. I father is not always going to give us what we ask for. After all, he knows what's best for us. How can dying of cancer and leaving our young kids be good for us.