Mally is right (but it's currently 90%). The reason for this is, if you are in a heavy fight and mash the heal key and buffer up 5 heals, and the first 2 heals bring you up to 100%, why have the bot waste power with 3 more wasted heals, so it will check your health before issuing you a heal... trying to be smart here

The bot will just give you that nice little message that you don't really need a heal ya fool!

Works out nice since the bot will be power efficicent and you don't have to worry about how many times you ask for a heal if you really need it.
What does worry me is Mally said 90-95% of the time - should be 100%... I have never had her miss a heal. If you bring the bot into the battle, sometimes they are not as timely as they might have just started a spell which has to complete before they heal you, which in battle can feel like a lifetime. If you had any logs where you asked for a heal but it never went off, I would really like to see it.
Rich