Eg. Inserting the charger plug in the socket every time one switches the laptop on. One day, she realizes that she didn't even remember when she inserted the plug. Similarly, there are a lot of activities like this that get stored in our memory.
The other answer uses the phrase Muscle memory. This is probably the best word I can think of for that. You would use it in a sentence like this:
"Propelled by muscle memory, she inserted the charger plug into the socket."
Subconscious is another good word. You use it like this:
"Subconsciously, she inserted the charger plug into the socket"
You could also use the word Absent-mindedly. This is when you do something without thinking about it properly.
"Absent-mindedly, she inserted the charger plug into the socket"
Those are all the words I can think of off the top of my head, hope it helps.
See mechanical (ODOL)
2 (of an action) done without thought or spontaneity; automatic. ‘Most curious of all was the fact that he made the same mechanical gestures no matter what he was saying.’
And, why, you already called it a habit, haven't you? (Ibid.)
1.2 Psychology An automatic reaction to a specific situation.
The ability to reproduce a particular movement without conscious thought, acquired as a result of frequent repetition of that movement.
‘typing relies heavily on muscle memory’
‘the secret to learning a technique like this is to do it over and over again until you have developed muscle memory’
‘For experienced players, muscle memory soon takes over from a conscious manipulation of these devices.’
As she is not consciously aware of having plugged in the charger, then this is done unconsciously.
One day, she realises that she had unconsciously inserted the plug.
This does not mean that she was entirely unconscious at the time (out cold, asleep or in a coma) as that would not be possible, however she was clearly unconscious of that particular action.
It is her subconscious that has made her do this. You would use this if you wanted to focus more on the state of mind during that moment.
One day, she realises that her subconscious had made her insert the plug.