The white liquid that you talk of is your girlfriends vaginal lubricants. These are produced when she is in a state of sexual arousal, and are meant to lubricate her vaginal passage so that sex is comfortable and enjoyable. There is absolutely nothing harmful in her vaginal fluids, if she is in good sexual health; and you can drink them to your hearts content. Even if she urinated in your mouth, it would do you no harm at all, and you might even enjoy it.
If your girlfriend wants to drink your semen, she can do so without any risk to herself. There is nothing in your semen (sperm) that can do her any harm at all. It is mainly water, and there is a small amount of protein, but nothing harmful. The only way your girlfriend can get pregnant is if you edge actually into her vagina, was somehow your seminal fluid finds its way into her vagina. Sucking your penis and drinking your semen will not make her pregnant, and if she likes doing this, you can give her all the encouragement in the world to do it as often as she wants.
I am always a bit concerned when people write in with questions like this. It indicates that you and your girlfriend are engaging in sexual activities without even knowing what you are really doing please use a little bit of common sense, and go online and read up about sex education. You could have answered all of your questions by a quick 15 minutes of research online. However, it's better to have asked the question and continue to do things in total ignorance.
Remember, if you don't want to make her pregnant, do not have vaginal intercourse with her without a condom, unless she is using a properly recognised method of birth control. Do not have sex with her and then tell her to take the the morning after pill, commonly called the I pill. It's not Andrew percent effective, unless used pretty much straight after sex, and it works by giving your girlfriend a huge dose of hormones, which upsets her natural menstrual cycle for maybe months into the future. As far as I'm concerned, there has been insufficient research in any possible long-term side-effects of using the I pill.
Now that you are armed with a few facts, I hope you and your girlfriend is a really enjoyable time together.