Unfortunately there is nothing at this point you can do to prevent transmission.  Your body either contracted the virus or it didn't.  Soap and water are helpful in killing the virus immediately after contact but if you've had time to type this post, then I'm assuming it has been more than an hour.

It's possible that you didnt but the likelyhood is fairly high if she had an active lesion and there was prolonged contact.  Pay close attention to see if you exhibit any symptoms and consider going in and getting a blood test for type one and type two herpes whether you show symptoms or not.  It's possible you already had it and didn't know.  In future, absolutely avoid any sexual contact when there are active lesions.  And it's always recommended to use a barrier method like condoms because she can still be shedding and transmitting the virus whether she's got a lesion or not.  It's called asymptomatic shedding.

Do some more research online, especially if you have a positive partner.  The stats say 80% of people have oral herpes so it's not surprising she did.  But it's NEVER a good idea to fool around with active sores.  And remember, even if you do test positive, genital herpes is something you can live with.  You can still have kids, and sex and a normal life.  It just takes educating yourself.

Best of luck.