Can a ladybug eat grape jelly?

Yes, ladybugs [Coccinellidae] can eat grapes. In fact, it's a big problem with the Asian lady beetle [Harmonia axyridis], which also is called the Japanese ladybug. It was introduced into the United States of America to control the Georgia pecan tree aphid [Monelia caryella]. It carried out its mission. But subsequently, it has gone on to terrorize the grape industry and to outcompete and devour native ladybugs.