graduation gift?  

I don't know much about your partner's sister, so this could be hard. It could be a book about preparing for college. I know that Christian families sometimes give the Bible as a present with the graduate's name on the front. A gift certificate to her favorite store would be appreciated, I'm sure. If you are close to her, you might take her out for a light lunch just to encourage her and let her know everyone is proud of her.

When my son graduated last year, his favorite gift to get was money. It was really appreciated as then he had the money needed to buy his college books. After his party, whenever I am invited to a grad party, I always give $$$.

Hi bcote!!!
You can buy for her a prepaid card gift about $50 or how much you want in any store, giftshops, supermarkets.
So she can use it to buy whatever her want and it is better than just give her plain money but still useful.

It is a special occasion so give her something related to that special day...
That could be anything you can imagine but you do it as a painting.

Send a picture to http://www.paintyourlife.com/ and they make it a unique awesome painting.

Karl

When I graduated I always appreciated money....but gifts stood out too...

Here's a cool gift site...they take real pictures and can put a name or message in it in cool ways..like a name or message written in clouds...birds spelling out a name over an ocean...a name in fireworks over a city skyline...cool stuff...lots of pics....these are prints that you can get as a print or a framed. Prices are nice too.
http://www.mypersonalprint.com

graduation it self is a gift. your parents bear the expenditure. which is more than a gift. you should not expect more. this is enough.