Ladies Dealing with head injuries

During a match a player took a ball to the head. She rubbed her face and clearly was slightly sore/stinging from the impact but when I checked with her she said she “was good”. The opposition continued to attack on the wing and the manager begins to scream “head injury ref”. I call play on but once again check in with the player who says she’s ok but is still holding her face.

Eventually the screams go on that much that I blow the whistle and wave the manager on to check on his player. Before he even makes it across the pitch, the player shouts at her manager that she’s ok and he then returns to the touchline but is still going on about how I should’ve stopped the game.

So my question is, at what point does someone who’s in slight discomfort due impact with the ball to the head become a “head injury” and is the player saying that they’re ok enough to keep playing or do you take that decision out of their hands?

Definitely not to the point of manager asking for it

At the point if you felt it was a head injury. Your gut feel will tell you and in this case it sounds like you didn't think it. Or the player is not responding (don't take a risk).

Did you ask the player to come of the field before the restart?

Gut instinct is usually right with head injuries. I had a nasty one in a youth game a few weeks ago where a player got smacked in the face by the ball. I checked on them and got zero response despite the fact they were looking at me (although they didn't look focused). I stopped the game there and then, and they ended up sitting on the pitch and staying there for a few minutes while being treated. My gut instinct was that they were probably concussed, and I probably could have been quicker on the whistle in that situation.
If the player looks fine and is responding appropriately to you, chances are they are ok. If they look a bit unsettled, aren't responding, or it was a big hit and you just feel off about it, stop play. Better safe than sorry.