dog door size

[fj45lvr]

hi,

I have a pet door to outside and wonder something: the door is a bit low for dachsund (and to fit below window above it....do you think it is at all harmful for the fila to have to crouch down to get through (on hip joints???) My 2 big dogs can get through it very fast if they want but they have to crouch down to do it . the door is 21" high and she is about 27" at withers

thanks