Upvote:1
Just having money isn't enough. Your friend has a son-in-law in Germany who is inviting her for some time. She probably isn't young any more. A suspicious mind could wonder if she wants to move in with her daughter and family and overstay. So your fried has to explain why she wants to come to Germany and why she will leave again.
But there is a special case for Germany. If the son-in-law signs a formal VerpflichtungserklΓ€rung, a promise to reimburse the German state for any intentional or unintentional overstay, that might make the difference in applications that might otherwise be denied. The son-in-law must have enough income to cover possible claims and may be required to post a bond.