Why is Thelma's mother in a wheelchair?

In the film Thelma, some parts show Thelma aged 6, others show Thelma starting university. Throughout the film, the cause of several events become clear during the course of the film:

- Thelma's sister has disappeared and died;
- Thelma's grandfather has vanished without a trace;
- Anja disappears.

All due to Thelma's powers or her grandmother's.

The film also shows that in Thelma's youth, her mother was walking around normally, but later in life, her mother is in a wheelchair.

Does the film explain anywhere how this happened?

Was it Thelma?
Was it Thelma's grandmother?

I may have missed it.