My granddaughter is 8 and is frequently losing things. It's the age. Unfortunately hearing aids are small and not easily found and are expensive.
Recognizing that she may take them out during the day give her a sturdy, small, attractive container to put them in and tell her to always give the box to a teacher.
You do want to encourage her to always wear them but you also need to be realistic about what she's capable of doing. How long has she had the hearing aids? Are they comfortable? Is she used to them?
My brother as well as one of the men I supervised both had hearing aids and neither wear them consistently. They tell me that their own voice sounds louder and like it's in a tunnel. They've been told that they have to wear them everyday in order to get used to them and the change they make in what they hear. These adult men never did stick with their hearing aides. After a few months my brother put his in a drawer and not used them since.
If kids tease her about the aids, arrange for a lesson in her classroom so that they learn how important the aides are and how their teasing affects your daughter. The teacher may be able to do this herself with your help. Perhaps you could invite a specialist who deals with hearing aides and this age. If the school has a counselor she is a good resource.
If it's possible to change her hairstyle so that it covers them more this might help. Or how about a wide knit headband that goes around her head and under her hair. Perhaps this could be placed so the aids are less obvious.
You could also try getting your daughter together with other kids who wear hearing aids so that she doesn't feel so alone in this situation. She'd have a peer support group.
My granddaughter, who is 8, is in both a Friendship group and a Homework group who were planned and executed by her school counselor. A Friendship group could be a big help. They get to know each other better and build supportive relationships. My granddaughter hums and sings a lot. She told me that she does this to take care of her feelings. She learned this ability in the Friendship Class.
This group got started last year when I told the counselor about such a group in which my daughter participated when she was 8. So it's possible that a suggestion from you would start getting support for your daughter.
I don't think negative energy of any sort would help your daughter. I would reward her when she brings the aids home; perhaps when she wears them home or for whatever behaviour you want to encourage and have a way of knowing about. Simple praise everyday is quite helpful. Along with that, acknowledge that you know how difficult doing this is.
Perhaps you could set up a routine in which she didn't have to wear her hearing aides everyday. Perhaps one day/week she could leave them at home. It could be possible that she'd see how helpful they actually are. Wearing them consistently for 4 days could give her the right to not wear them the day after that. Perhaps include her in deciding how to set this up. Making a child part of the decision making process helps to make them feel less like a victim and more like she's important and does have some say in her life.