From my blog, Rannygahoots: http://rannygahoots.blogspot.com/2012/05/whats-point.html
What's the point in inviting her if she's only going to cancel out on us?
What's the point in asking, if she's just going to say, "if I feel up to it."
What's the point in calling/visiting if she's going to be too tired or distracted to talk for long?
The point is that she wants to live her life, even if that means making plans and having to cancel them.
The point is, knowing she's still included and her friendship still valued is priceless and helps her get through the rough days. She hopes her friends realize that the invitation means the world to her, even if she can't handle going out or is busy with other things.
The point is that although many things can interfere with having a coherent, cohesive conversation, it doesn't mean that she won't still have fun, make wonderful memories, or find joy when spending time with friends.
Whether it's due to having small children, health issues, no transportation, or anything else that might hinder her ability to be socially available whenever she wishes, she wants to enjoy her life and her friendships. She wants to live her life to the fullest NOW. She wants to know people care about her. And it probably breaks her heart when she has to cancel or can't participate, but not as much as it breaks her heart to not be invited, or called, or visited.
Give your friend a call. Invite yourself over to treat her to coffee or tea. Give her a break. Give her a hug. Give her a hand. Bring her a meal. Include chocolate. Or wine. Or both. Let her know that you miss her. Listen and offer love, even if you don't understand what she's going through.
What's the point? Friendship.