While she is sleeping, we decided to wake her up.
That's simply wrong. You are mixing a present tense with a past tense. You could say:
While she is sleeping, we decide to wake her up.
This is pretty rare usage, though. In English we almost never give a narrative in the present tense. Present tense is primarily used to, (a) describe something literally happening right now. "Where is Bob?" "He is out to lunch." Or (b) to describe a continuous state. Like "Paris is the capital of France." It has been for a while and it is now and it probably will be for some time in the future.
More likely would be:
While she was sleeping, we decided to wake her up.
Also, when you have a conditional expression referring to a future event, you use the present tense, though logically you might think you should use the future tense.
WRONG: While she will be sleeping, we will decide whether to wake her up.
RIGHT: While she is sleeping, we will decide whether to wake her up.
(There's probably a name for this, it's not really the present tense, it's some kind of future conditional tense. But I don't know the name.)
If the stock market goes up, I can retire early.
Unless you stop acting irresponsibly, you will never get a good job.