Thank you @Anonymous_ and @TomD8 ! This is very useful information.
So if I understand this correctly: What my mother is planning to do is a "transfer with retained life estate": She will have the right to live in the apartment for the rest of her life or even rent it out to her benefit alone. There will be also certain conditions where she could claim the gift back.
However, I do not see how this apartment would still be part of her estate when she dies, as it will already be in my name at the moment of her death.
So how can the two concepts be reconciled in one contract? A retained life estate that would still be part of a "death" estate. At least by German law, I don't see how this could be done legally.
