chienbizarre - pat yourself on the back for taking some time to get some facts on herpes. Then, pat your partner on the back for talking to you about her herpes diagnosis. The fact that you are seeking information and the fact that your partner has discussed the situation says a lot about both of you and the relationship. Specifically to her, having the discussion shows honesty and trust on her part and both are good for any healthy relationship. Coping with herpes in a relationship can sometimes take time, but this is often due to all the misinformation about the virus. So you're taking an important step by simply educating yourself. Rest assured that we talk with couples each day for whom herpes has become nothing more than a minor thing in their relationship.
To follow up on betsyb's comments, your partner's genital diagnosis of HSV-2 has no bearing on her mouth. Even if she is experiencing genital symptoms, she could still kiss or perform oral sex during that time. Likewise, if you are experiencing an oral symptom, it would have no bearing on your genital area.
In terms of you getting HSV-2 orally or her getting HSV-1 genitally (with you likely having HSV-1 orally) from oral sex, it's highly unlikely for someone to get both types of HSV in the same location. Especially in your situation because both types are already where they want to be. The site of preference for HSV-1 is the mouth while HSV-2 prefers the genital region. In addition to that, you both have an immune response that makes "reinfection" of any kind unlikely.
Regarding the relationship overall, know that you can have the same level of intimacy and sexual activity that any couple can. There is nothing that you can't do. Don't get me wrong - there is a possibility of you contracting genital herpes. But, that's a possibility for any sexually active person anywhere. Anyone who has had or will have sexual activity assumes some level of risk for contracting herpes or another sexually transmitted infection. There is no such thing as "risk-free" sex for anyone, anywhere. That's why not having sex when genital symptoms are present and using latex condoms are good recommendations for any sexually active couple regardless of whether herpes is part of the equation.
Back to herpes specifically, the fact that you know your partner has the virus and that you are educating yourself would reduce any risk of transmission. Unfortunately, it is not possible to accurately quantify the risk of passing or contracting the virus. To do so, there would need to be a study/clinical trial that provides that information and there are simply too many variables that a study/trial cannot account for (is a couple having sex once a day, twice a week, once a month; are condoms being used consistently, never, off and on; is the sexual activity for two minutes, an hour; does a partner already have oral or genital herpes; are antivirals being taken; individual immune systems, etc.). But, as you mentioned you already know, there are ways to reduce the risk. Simply abstaining from sex when genital symptoms are present would reduce the risk considerably. Using condoms and your partner taking Valtrex would reduce the risk even more.
It would be a good idea for you to get tested. If you have ever had sex/genital contact before, you could already have genital herpes and all this is kind of a moot point. As you may have read on other posts, it's not uncommon for someone to unknowingly have herpes - as many as 90% of individuals with herpes don't know it. If you're interested in getting tested, you can talk to your health care provider. Make sure to request a "type specific IgG blood test." You can get testing info at: http://www.ashastd.org/testinginfo.cfm
Finally, you mentioned not wanting to give your partner up. Don't. You said she is fantastic, so if the relationship ends, let's hope it's for a legitimate reason and not simply because one of you has herpes.
Apologies for the long post.