I think her chakra control being so perfect is precisely WHY she can do what shes doing.
She is the prime example of Maximum effect for minimum effort. AndNo she does not have nor need enormous chakra reserves.
in point of fact I believe that a lot of people drastically underestimate her natural reserves as it is. She was never weak in that regard she just never had any special jutsu to use it on.
Sakura I would actualy postulate had at the beginning what I would call average chakra reserves possibly slightly below average reserves for a ninja of her age and ranking. those reserves expanded normally to chunin levels and are now I would say Normal Jonin levels.
But because of her Near perfect control she is able to use jutsu and skills that would leave most shinobi doing the same exhausted.
Not to mention that she did not restore Narutos Chakra she simply healed him back to full health.