There's a gap in what you're asking vs. what's available.
First off, what you do NOT want to do is add HER phone number to YOUR Apple ID. If you do that, she will start to get all your text messages, and will be able to send message as you. I don't think you want that.
Since your daughter has her own Apple ID/Account, she has her own identity, which is a start.
You've setup a Family Sharing account, and added her as a child. That's step two.
However, Family Sharing does not give you unfettered access to her account. It gives you the ability to control which apps are installed, limit screen time, share locations, and share iCloud resources such as iCloud Drive (storage), Apple Music, Apple Arcade, and the like, as well as shared purchases in the App Store.
What it does not do, though, is give you unfettered access to her data, including her messages, photos or contacts. You can not see her messages or other private content without logging into her account.
If you set her password (and she doesn't change it), then you're able to log into her account on your device and see what she sees, but it won't automatically happen.