You should have spoken up, to the Parent or to the child.
If it were me, I WOULD have. Definitely. I would have looked at that girl, with firm stealth eyes, and said "stop, you HURT my daughter... she is bruised... if you do not stop, I will call the manager... where is your Mommy???" And if the girl then ran and tattled to her Mom, then so be it... I would have dealt with her too, and saying that her girl hurt my child on purpose... and it has to stop... the girl is bullying my child. AND there are bruises to show for it.
You role play with her.
You give her the words or sentences to use, to actually say. ie: stop it, that's not nice, you hurt me, go away, I will tell the Teacher etc.,
Kids this age need to know the ACTUAL wording to say... they can't think it up on their own.
You TEACH her, to always stand-up for herself, and to use her voice... using a "stern" voice, a "firm" voice etc., and then do it to show her... how to use her voice. And her eyes to look at the person, firmly.
You TEACH her, what is right and wrong. What is "bullying." What it is to go someplace else (if possible) to avoid bad people/kids.
AND, that as a parent, that YOU actually show her how. When my daughter has had incidents (being bullied or picked on or hit) ... I have actually spoken up... and DIRECTLY talked to the Teacher or child or the Parent. I do NOT give excuses for that behavior... I SHOW my daughter, and have her by me, while I do this. It gives the child, a "lesson" in how to correct wrongness.... and it gives them confidence. It SHOWS them, that their Parent KNOWS HOW to handle it, too. And I explicitly SAY to my daughter... that this WAS a wrong behavior by the aggressor. My daughter knows. And my son too. I am NOT SHY, in doing this. Using all my skills of diplomacy and firmness in my speech... in dealing with these trouble-maker kids and Parents. My Daughter's Teachers have actually praised me... because they say not many Parents will speak up... meanwhile their kid is still being picked on etc. But I always do it with as much diplomacy as possible, gauging the situation.
For their respective ages, my kids WILL speak up... and even my 3.5 year old will actually even "correct" an adult if they are not nice. And I am proud of him. He KNOWS right from wrong, mean-ness v.s. nice/caring behavior. I have taught them these things from about 2 years old.
Kids, need to learn how to "handle themselves" by seeing it in their parents too. AND, you role-playing with them scenarios. And give them the words on HOW to say it... to speak up for themselves. It takes PRACTICE. It is not instinctual in all kids. Nor adults.
My daughter, takes Karate. SHE wanted to. She loves it. There are many benefits to it.
Both my kids know, how to defend themselves, verbally and physically... but not to use it as an aggressor.
You need to teach them that.
all the best,
Susan