Hi,
I confess I'm never entirely sure whether, in these circumstances, an award is of the care component of DLA or whether it is AA. But either way, the fact that your mother gets an award for care - whether it's called DLA or AA - will not mean that her mobility component ends.
Though, i should add, as always, that when you notify the DWP of a change of circumstances there is always a possibility that an award can go down rather than up.
Good luck,
Steve
Nothing on this board constitutes legal advice - always consult a professional about specific problems