Check the reviews on any camera before buying.
$500 is a good start. If your GF is super serious, you may run into a situation where she would prefer A, but you bought B.
Another option is to consider pooling resources. If she can come up with $500, then that's $1,000 towards her goal. That puts a mid-range DSLR and decent lens on the table. If others can kick in, perhaps she can get into a full frame DSLR with the Canon probably being the most affordable.
The most expensive route is spend $500, not be satisfied, trade up, etc.