your photographs are fine, i wouldn't worry too much about it.
a lot of people judge photographs by what they are used to seeing and making.
we all come with our own complex set of samsonite luggage so to speak.
i am sure your mom knows what she likes and knows what she doesn't like ...
and she is speaking from there .
there are all sorts of "rules" when it comes to composition. but the whole point of rules
is to break them. your work is very good, and the group you submitted to knows it too.
parents are parents, and sometimes they don't like things outside their " comfort zone ".
congratulations by the way !