When people come out as gay, it's not a "change". It's just coming to a realization that sometimes takes a while because young boys and girls are most of the time basically "taught" that they're supposed to like the opposite sex. Then you have denial and so on that can delay it further (see Iceman, for an X-ample).
In Laura's example, there's also the fact that she was robbed of a normal childhood and didn't socialize much until recently. I'd buy that it would take her a while to figure these things out.