You cut that risk in half if she
uses Valtrex daily, or if you two decide to use condoms. If she is already using the Valtrex daily, you are getting a protective effect from that, so your risk is down around 2% PER YEAR. That's not with each episode of sex, it's during your sexual relationship over a year. If you throw both of these methods into the mix, your risk, as you can imagine, is extremely low.
Oral sex is not really something to be concerned about.