Balloons with photos of memories tied to the bottom is a sentimental and thoughtful proposal idea. Let her pop all of the balloons to find the ring. You can fill the rest of the balloons with sweets, glitter or flowers.
Remember: Doing Nice Things for your family is just as good as for strangers. Leave a nice unexpected note for you kids or husband, a roommate- or even at your siblings or parents house when you visit.