Girl hasn’t opened my message but has since commented on my posts? What does it mean?

I vaguely knew this girl when we were at school and we’ve been Facebook friends for a long time and every so often she would like some of my posts but this would be the most we would interact.
A few months ago though, I bumped into her again when a mutual friend of ours invited us both round to a do at their place, and I met her again the following week under similar circumstances. We got talking and seemed to get on well, so much so that I decided to send her a message asking if she wanted to meet up. However, she never even opened it, never mind replied, so I took that as a flat no and moved on.
A few months later though, she posted happy birthday on my wall and commented on my latest post about my holiday saying that she hoped I’d had a good time (literally no one else had commented on it). She’d never done either of those things before and I presume it was us meeting again recently that was partly why she felt she could. But then why would she do this and yet not even open my message? I took that before as her saying that she didn’t want to interact with me online, yet she goes out of her way to post on my wall and comment since then, so I feel like I’m getting mixed signals.
I don’t understand women sometimes. Is this normal? What does it mean? Is it worth messaging her one more time?

maybe she didnt see your message request ? normally id be like shes ignoring you but doesnt seem like it

Maybe she's nervous texting you. If I like someone, or want someone's approval I hesitate a lot when that person texts me. I think you should text her again, try to keep an open convo

She likes you

Maybe she wants to retain friendship but not romance. And perhaps she was able to see the message without opening it. Or just maybe she missed the message. Could be worth another go, better still to suggest something in person. The wait for replies to messages is always excruciating

Probably didn't see is all try again or maybe call instead up to you

Honestly, if a crush messaged me first, I’d be thrilled and very keen to respond, but I guess I’m different. Interesting suggestion though. Although it has been three months now since I messaged her. Is it possible she could ignore it for that long if that’s the case and forget about it?