I need to ask you a few questions to better assist you.
How much weight do you think your little girl has lost and what time period?
What diet is she on?
Do you see her stool samples and do they look normal for her? Anything in there that resembles white rice?
How is her activity level? Happy/depressed?
Is her hair thinning?
Please answer each of these questions. Thank you
How much does she typically weight when healthy?
Since that is a drastic weight loss, that does concern me. The dewormer that you have used, does it do tapeworms as well? Some dewormers do not treat for tapeworms.
Another question, what aggression behavior has she lost?
Is her stool samples normal or does she have diarrhea at all?
She will normally try an bully the shepperd but since she not felling herself she don't try to bully any more. As a matter of fact the shepperd sometime tries to bully her. On the de-worming medicine i'm not sure. It said several types but i recently trashed the package. I'll check her stool again and get back to you with an answer.
It does sound like that she is not feeling well too. That does concern me. With a drastic weight loss such as 25 pounds, there could be more going on.
I would suggest that you take her to your vet and have bloodwork done. Since she is 6 years old, it is a good age to have that done anyway since she is large breed. Let the vet know that you want to check her thyroid as well. This can allow him to better evaluate her because a problem with the thyroid can cause similar signs.
Here is a website that explains hyperthyroidism:
If you do see that she is having white little rice grains in her stool, then you can give her some more dewormer but make sure it treats Tapeworms.
If she is having diarrhea, please let me know. But I do recommend a check up at your vet for bloodwork. It sounds like she is having some internal issues that we can not see.
Thank you and Please keep me posted on how she is doing. Let me know if you have any other concerns as well.