Female here, I just created an account to answer this actually.
From what I understand she was actually stronger than you, then, if anything, she should be the one protecting you.
It is not "more acceptable" to protect a woman that doesn't need it than it is for a man, I'm sure if it was a guy you wouldn't have protected him and that's totally illogical.
Now, to answer your question, if it were me in this situation, if I felt the guy was weaker than me I would have protected him. If he tried to protect me I would have been grateful if he was stronger, mad if he was weaker.
And to further answer, if I am with a group of peoples and that a stronger person (man or woman doesn't matter) protected me when there was someone weaker to protect, I wouldn't accept it.
If anything acting all chivalrous when you are weaker make it look like either you consider every woman as inferior to any man or that you have some kind of crush on her and try to impress her.
I'll just go with an example that doesn't take into account strenght at all. Your question is a bit like "Do you think we should always hold the door for women ?" to me.
Of course you should, when someone is before me I expect them to hold the door until I'm at arm lenght for it. But if I was a man I would expect as much, that have nothing to do with chivalry but with politeness and common sense.
You should always hold the door for peoples behind you, no matter their gender or age.
And I think the same, you should always protect the weakest peoples first, no matter their age and gender.