The way you invite a bride to her bridal shower depends on whether or not the shower is a surprise. A surprise shower will take a great deal of careful and clever planning to trick the bride into showing up at the right place at the right time. If the bride does know about the shower, the way you invite her will depend on the tone of the shower and wedding, casual and fun or formal and classy.
Co-conspire with the bride's mother, sister, best friend or fiance to arrange a date with the bride, that unbeknownst to her, is actually a ploy. This way, the bride doesn't make plans that contradict the shower. For example, her fiance might suggest they meet his mother for lunch.
Pretend something came up at the last minute. The person who originally made plans with the bride should cancel the plans. For example, on the morning of the occasion, have his mother call and say she has a headache and wants to reschedule.
Have the fiance suggest they go out to lunch anyway and escort her to the place of the shower. The advantage of incorporating the mother-in-law lunch element and canceling is to throw her off track. If her fiance simply suggests they go out to lunch one weekend day, especially when it's planned in advance, this could make her suspicious.
Take her to the location of the shower, and instead of being seated for lunch lead her into the room of her shower, completing the surprise.
Set aside one of the bridal shower invitations and leave it blank.
Replace the traditional greeting of "You are invited to a bridal shower" with a fun statement such as, "You are invited to be showered with gifts, love and attention in celebration of your upcoming marriage."
Include the pertinent information such as the location, date and time.
Write under RSVP, "The receipt of this invitation is your RSVP. Attendance is mandatory," to add some humor.