Yeah, im not psychologist but I play one on the internet and here’s what’s happening:

• you’re afraid when your gf graduates she’ll “make some big life choices”
• you wanna lock her down now while she’s still a student so she doesn’t think “ima PHD! I can do better!” (Not saying she’s like that)
• when she said not ready to look at engagement rings it added to that concern
• when the friend did the same engagement ring it gave a convenient outward place to focus that tension: oh noes, the perfect ring is despoilt!

Fortunately, the engagement is perfect because of the people getting engaged and this ring stuff is gonna be water under the bridge. Just get her the same one if you want (idk) I mean, if it’s nice it’s nice - there’s wayyyyy to many people with engagements for them all to be unique and what’s so magic about unique anyway?

Sounds like you might benefit from having a talk with your gf about what she sees for the future, when to get married (if she sees that in future), kids, where to live etc.