You've had your speech written for years, but the bride didn't ask you to give one? Accept it, don't fight it. You may not understand her rationale, but she made her decision. If you feel strongly about one of her wedding choices, you can always ask her about it. Just be respectful, open-minded and accepting of her response.
On the other hand, maybe she asked you to say something and give a toast, but you'd rather have the flu than speak in public. Stretching outside your comfort zone can be tough. But it's her day, so go with it, follow her directives and do your best.
Keep in mind, though, that the bride doesn't get to steamroll over your personal boundaries, whether it's your budget, morals or time.