AITA for not messaging my friend first?

I (19F) and my other friends, for safety I’ll call one Tia (19F) and the other Fiona (21F) were all on this group chat on discord. Fiona was upset because I didn’t respond to her message first and she said she should have gotten a response first.

For backstory, we all found each other a month ago on Roblox via Adopt Me, a very popular game where you collect pets and trade to get better value pets and other items. I was chatting to Tia, I hatched the pet she wanted and I was feeling charitable and gave it to her for free and we then started chatting for around an hour. We then encountered Fiona. We all hung out in my house on the game and just started chatting about what pets we have and values et cetera. We all decided to add each other on discord so we could all stay in touch. Fast forward to yesterday, I was pretty busy trying to organise my room and move furniture out as I have a pretty hefty project. I wasn’t looking at my phone and Fiona sent a message saying hey and that she was able to book driving lessons, I didn’t see that message nor did it pop up on my notifications board. I finally settled down and I saw that Tia typed in the chat, so I responded to her message BEFORE I saw Fiona’s. I did say hey to her earlier and asked how she was but I just missed the message when she mentioned about her driving lessons. When I logged back onto Discord to see the chat I saw that Fiona had left the group, both myself and Tia were confused so we went to message her. Fiona then went on to explain that she felt hurt that I ignored her message and messaged Tia first. I apologised to her for not seeing the message and I was trying to convince her to join back to the group chat. She refused. She was telling me things like that Tia told her she was overreacting a bit and then proceeded to call her manipulative and aggressive and even said "wtf is wrong with you" when Tia was expressing how she felt. She also went on to say to Tia that "I thought you were different" and "You’re just like everyone else" to me that sounds like guilt tripping, correct me if I’m wrong. Fiona was saying to me that she felt ignored and all I could do was just apologise for not seeing the message. Fiona has also mentioned she is a sensitive person but as a sensitive person myself, I even think it was just a bit of an overreaction. For the rest of the night she continued to ignore us.

Fast forward today now, first message I received today said "I mean fair enough" I then told her that I’m not mad at her but I was frustrated that she left over something small and that we both apologised. Fiona then went on to tell me "my irl friends and bf both said they would leave if that happened to them, idc abt it anymore so im just saying fair enough". I then typed to her "Suit yourself then. Cya" and then I tried to send another message but she had blocked me by then.

So reddit, am I the asshole for not messaging Fiona before Tia?