You've probably already read through the Guinea Lynx info, but here's a link just in case:
Guinea Lynx :: Reproduction. May I ask why you didn't adopt instead of buy from a pet store, seeing as you "hate" stores? I'm sorry you have ended up with an unexpected pregnancy, but I do have to say it happens all the time with most pet stores. I have no idea what options are available to you for adopting way over in Germany, though!
At any rate, the important thing now is to do what you can for your piggy. Provide lots of fresh veggies daily, and you can supplement her diet with alfalfa hay for extra calcium. It's always a good idea to "baby-proof" the cage as she gets closer to her due date- put up an extra 6" of coroplast, or use more closely-spaced shelving or mesh to make sure the babies can't fit between the cage bars. Keep her bedding clean and try not to stress her as she near her due date. You can check her pelvic bones so you will have an idea of when she will give birth- during the last 48 hours her bones will spread to about one or two finger-widths apart to make room for the babies. Some people have a hard time feeling this themselves, so it helps to compare them with one of your non-pregnant piggies first. I was able to tell when my girl was about to give birth by checking the pelvic bones first.
I hope that info helps a little, and I wish you the best of luck with your new girl. Let us know how things work out for you. Oh, and when the babies come we'll be expecting pigtures ASAP!