My girlfriend came home with multiple scratches and a few light bruises on her body. uhm... help?

she went out with her best friends in the afternoon yesterday. i didn't see her till she came home at about 1:30 in the morning. when she got back into the house she had scratches (or what looked like scratches) on her arms, legs, forehead, stomach and back. she also had some very small bruises (maybe like 5 in total) on her legs and arms. there was a blood mark on her one arm and i think it's cuz one of the scratches bled cuz it was red too. i walked closer and gently grabbed her arms and asked her what happened. she jokingly said "nothing, don't worry about it (my name)" with a grin on her face then kissed me and walked to our room to put her bag away. i asked if she was ok and she said she was. i then asked her if she did something that hurt her and she said no. it's now 9:40 the morning and she's still sleeping because we got to bed very late. when i looked at her scratches before i left our room they look more red than they did when she first came home. I don't know if it's cuz of oxidation of a kind of wound or what it is. the bruises look darker because they're forming more. i know this is very minimal information to help figure out what happened but that's all i got to say. what do you think she did? please don't say she had violent sex with another guy because that's just immature and childish to assume and she wasn't even with another guy; she was with her best friends who are girls. it almost looks like she fell and if she did... I don't know where that would cause that. what's concerning me is that she isn't telling me what happened but rather telling me not to worry about it, that she's fine, etc. any ideas on how i can get her to possibly tell me what happened? i won't rage out on her or make fun of her because i'm not like that and not that rude
My girlfriend came home with multiple scratches and a few light bruises on her body. uhm... help?
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