Chances of her getting seated are very slim, especially at Ohana.
Yes you will be sat at a 4 top because there are 3 of you, so adding a chair is simple, at least this is what people think, but it is wrong. All restaurants have fire codes they have to go by and if a place is booked they can't add people because it would break the law.
Also Ohana is very popular so it will most likely be booked, then add
free dining in there and it makes the chances even slimmer.
Sorry I would go ahead and keep trying for an adr, meantime I would make arrangements for her to dine elsewhere (maybe Kona, it is right next door) and meet up after dinner. Or maybe she can eat early and take a relaxing stroll on the beach and have a cocktail while you guys eat.
Either way, I would just be prepared for her to be turned away, sorry.
Have a good trip and enjoy yourself!