Scared of My GF's Reaction to Something Small, Is It Normal or Red Flags?

So, I'm a 24M and I've been with my girlfriend (Lola, 23F) for four years. Recently, I’ve been feeling a little uneasy about her reactions to small things. The other day, I didn’t respond to her for about 10 minutes because I was snapping my best friend (Amy, 22F) on Snapchat, and I did not saw her notification. Lola saw my Snap score go up and got upset.

At first, she didn’t say anything about it but started making barbed comments and periodically ignoring me. It wasn’t until about 3 hours later that she finally told me what was wrong. I honestly felt frustrated because I had no idea what I had done wrong until then, and the whole situation left me feeling really uncomfortable. I called her a stalker and said I was terrified of her actions and she just laughed at me. She said I got mad at everything she brings up to me these days and that's why she didn't immediatly tell me.

Her behavior of stalking my snap score for 10 minutes felt a little erratic, and I’m starting to wonder if this is normal or if I’m missing something. I really care about her, but I’m getting concerned about how she’s reacting to small situations. Am I overthinking this, or is this a red flag?

TL;DR: GF (Lola) got upset when I didn’t respond for 10 minutes because I was snapping my best friend (Amy). She saw my Snap score go up, got sad, made barbed comments, and ignored me for hours without telling me what was wrong. Is this normal, or should I be worried about her behavior?