How to get 1-2 qm stuff from MI USA to Germany in June 2019?

Does anybody know, what`s the cheapest way to get some personal stuff (ca. 1 qm/ 100 kg) moved from Michigan to Germany?
We live in southwest Germany. Our daughter`s high school exchange ends after 10 month this June and we will pick her up from Detroit. We fly and are afraid, all her stuff (like heavier/ bigger presents) is too much to get on the plane for a reasonable amount of costs. Every person has 1 suitcase with 23 kg included. 1 additional suitcase is around 100$ each person. Another suitcase is 150$ each person... And we wanted to shop too during our 3 weeks stay in the US...
I was checking USPS and found 200$ for a 32 kg parcel.
Than I was checking different transport companies for getting a box, 1-2 qm/ 100 kg by see to Germany, but either they didn`t answer at all or ship only from NJ or it was much higher costs.
Great would be, if somebody would move anyway about the end of June from Flint, MI/ Chicago/ Detroit or similar and we could add our 1 qm stuff into his container and pay this person.
Or has anybody a smart idea for that problem?

USPS is about the least expensive shipper for small loads. Finding someone to add to a container as in Beipack is a needle in a haystack. Personally - for liability and customs I would not add someone's moving goods to my container.
You can check with some of the big international carriers such as Schenker. Be prepared for sticker shock and time for delivery.
Leave behind what is not a critical item. Offer an additional suitcase or two. It is the cheapest option.

Maybe she could sell everything she doesn't really need to take back to Germany on Ebay and only take the extremely personal items and gifts back with her. Selling on Ebay would take a little time and effort, but it's  an option.
I would be wary of trusting my things to a stranger to add to their container and finding someone may be close to impossible as well.
I found this, but you may want to find independent reviews online to see if the site is trustworthy. It's a student shipping website.   https://www.sendmybag.com/student-shipp … gLKJ_D_BwE