Why does my girlfriend text me after we had argument when she could just tell me then?

My girlfriend isn't much of a talker, she's quiet keeps to herself and barely leaves her house. I mean I found her in a hardware aisle reading boxes of screws cause she was embarrassed to ask for help but anyways we were over at my house watching a movie. She was on her period so she was in pain and curled up on me, she is fairly small and looks like my kid whe we are next to each other. I was saying it was hot I had a rough day and the heat was adding to my frustrations but her being there made my day a lot day. She got up I asked her y she got up, she said I was hot and started taking off her sweater. I wasn't yelling at her I just wanted her to lay down on me cause it made me feel better. She took her sweater off still looking at the movie and was giggling I don't remember what she was talking about on the screen but then I raised my voice a bit and told her 'shut up, just lay down that's what u need to do' it sounded a lot bossy so I asked after 'if laying down isn't what I wanna do'. She froze and just stared at me she was about cry she said that wasn't very nice and she was just taking her sweater off cause I was hot. I sighed and she sat back down and laid back down on me but she was on my stomach not on my chest. Then she started scratching her nose. She does this when she's said, I told her to stop sulking and she stopped but she wasn't talkative like she was a minute ago. I asked if she was upset and she shook her head so I let her be. Then she texted me later that she didn't like being yelled at and she was sorry for going quiet she didn't wanna talk and end up crying. She could've told me so we could address it immediately then but she choose to text me later she's done this before plenty of times. Texting me when she didn't like how I acted towards her or stuff I said. She can just talk to me.

Why does my girlfriend text me after we had argument when she could just tell me then?
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