My advice is drop this whole line of thinking right now, unless you want to be disliked and possibly have people dropping out of your wedding like flies.
Your wedding isn't the center of life on planet Earth, first of all. As others have said, it means a lot to you but not that much to anyone else. It in no way justifies you attempting to control anyone else's decisions on when and how to share the good news going on in THEIR lives.
Worrying about hogging every molecule of attention for yourself sounds like not even being mature enough for kindergarten, let alone for marriage, tbh.
Even if she did announce her engagement during the toasts at your reception, so what? Who on earth cares? Just let her do it, if she wants to. Smile and congratulate her and clap for her. Let other people tsk-tsk about it if they want to, while you show all how gracious and angelic you are.
You should ONLY worry if she and her fiance rush down the aisle after you and your fiance, attempting to get a two-for-one on your entire wedding and reception. No, never mind. That would be hilarious and make yours the wedding of the century, still discussed decades later. So, no worries at all.😂
Seriously though, if you care about your wedding so much, the first thing to kee firmly mind is how you come across and what people will remember about your attitude and behavior. Self-centered and jealously demanding all the attention for yourself is not the look you want. Best wishes.