Don't be letting her think the rest of us love them or she'll end up feeling inadequate or that something's wrong with her.
This.
Don't you think she might resent you somewhat if you spin her all these glorious tales and then she starts her periods and realises it's fucking painful and hideous and you didn't bother to tell her all the nasty stuff so she had no chance to mentally prepare to face it?
Knowledge will empower her. If she's not prepared for the reality and what she can do to help herself then she has no power and is not empowered. How incredibly distressing and disempowering to be psyched up for glorious womanhood only to discoverr when it arrives it's nothing like the sales pitch and you have no idea how to handle it, cope with it, endure it, or make it better. You specifically say you want her to feel empowered, so shouldn't this be your focus? Giving her power. That's what the word means.
Empowerment isn't about glossy positivity slogans. It's about having the knowledge, tools, and ability to change the things causing you problems. To influence your own life and circumstances. So be real with her, and equip her for the things she'll face. Talk to her about all the different ways to manage pain, the ways to manage activities, the ways to not let them hold you back, the ways to still feel confident, the ways to keep herself prepared, where to turn if it seems to all be going wrong, the ways to cope psychologically (e.g. Talking and bonding with others, counting down until it's over...!)...
You can show her it's not a terrifying nightmare, by being honest and showing all the ways there are to cope with issues and symptoms. By sharing examples of times when you felt like your period was going to ruin something but you made it through, or when something embarrassing happened and what you did in response and how you feel now about it. That also gives her the chance to think about what might make her feel more confident and in control, and what would help her if she has periods like yours, for example. Then you can prepare.
As an example, I still remember being devastated the first time I was on during a school trip, but that is a useful experience to chat through and let her raise worries and concerns and problem solve - rather than considering it for the first time when it's actually happening and she's too upset to think calmly. Plus, if you bring up the difficult stuff (from a survival skills perspective!) it gives her a chance to talk to you about any worries that she might feel embarrassed to raise if she thinks she's supposed to be 100% excited and enthusiastic 100% of the time.
Don't just spin her all this glories of womanhood stuff without any practical tools. Pain is all natural, dying from infection is all natural, but nobody tries to say they're positive. False positivity isn't empowerment.
Oh, and I can't think of any woman I've ever known in real life who's talked about her periods as some great positive wonderful thing. I don't remember any of the girls at my school who were excited in advance, still thinking periods were great once they actually started. It won't be great if she feels deceived.
The positivity is in all the ways you can cope with them and take control of things, not in periods themselves.