Well, if you're serious about teaching her logic skills ;) (I've ignored two dollar bills for simplicity. It should be trivial to add it)

#!/usr/bin/perl

use strict;
use warnings;
use AI::Prolog;

my @bills = qw(Fifties Twenties Tens Fives Ones);
my $bills = join ',', @bills; # don't use $prolog->list because these 
+are vars

my $program = <<"END_PROLOG";
change([ $bills ]) :- 
    member(Fifties,[0,1,2]),
    member(Twenties,[0,1,2,3,4,5]),
    member(Tens,[0,1,2,3,4,5,6,7,8,9,10]),
    member(Fives,[0,1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20
+]),  
    Total is 50*Fifties + 20*Twenties +10*Tens + 5*Fives, 
    Total <= 100, 
    Ones is 100 - Total. 

member(X, [X|_]).
member(X, [_|Tail]) :-
    member(X, Tail). 
END_PROLOG

my $prolog = AI::Prolog->new($program);
$prolog->query("change([ $bills ]).");
while (my $result = $prolog->results) {
    for my $i ( 0 .. $#bills ) {
        print "$result->[1][$i] $bills[$i]";
        print ", " unless $i == $#bills;
    }
    print "\n";
}
__END__
# Beginning of output:
0 Fifties, 0 Twenties, 0 Tens, 0 Fives, 100 Ones
0 Fifties, 0 Twenties, 0 Tens, 1 Fives, 95 Ones
0 Fifties, 0 Twenties, 0 Tens, 2 Fives, 90 Ones
0 Fifties, 0 Twenties, 0 Tens, 3 Fives, 85 Ones
0 Fifties, 0 Twenties, 0 Tens, 4 Fives, 80 Ones
0 Fifties, 0 Twenties, 0 Tens, 5 Fives, 75 Ones
0 Fifties, 0 Twenties, 0 Tens, 6 Fives, 70 Ones
0 Fifties, 0 Twenties, 0 Tens, 7 Fives, 65 Ones
0 Fifties, 0 Twenties, 0 Tens, 8 Fives, 60 Ones
...
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