She defiantly looks a little pregnant, probably around 2-3 weeks (I am no expert! However when I got my two Guinea Pigs October 18, 2016 and my Sow looked just like your cute little girl and now she is huge and defiantly has at least two babies moving around inside her.)
I have stayed up my fair share of nights these past few weeks researching everything Pregnant Guinea Pig and a lot of people have different methods, but their opinions remain the same;
The sow needs extra vitamin C, either through special dried cookies found in most local pet shops (it will list Guinea Pigs on it and likely come in a small clear plastic jar with a grey label). Or you can accomplish the same effect with a cup of fresh veggies, fresh water and Timothy Hay daily (make sure you clear away old, uneaten food to avoid mold around your piggies.) I mix my Timothy hay with some alfalfa hay now, to give her a little extra boost of vitamin C, along with some romaine lettuce, red & green bell pepper pieces, parsley, cucumbers and radicchio lettuce, 1/2 a cup in the morning and 1/2 a cup at night, all cut up in a little piggie salade for easy charing with her cage mate.
If she is resting a lot there is no need to worry, she is very tired carrying what is more then likely at least 2 pups. She will be tired from sharing the energy and the strain that they will put on her organs. As long as she is eating and drinking and responsive, she is just fine. If this is her first litter she is likely to have 1-2 pups. The average litter size is 3 and in rare cases with seasoned breeder sows they can have up to 7 pups. The larger the litter the smaller the pups, naturally, so until you start to see movement and can feel her babies it will be hard to guess how many she has base on size alone.
Make sure she is comfortable, I would recommend Fleece, mostly because when I made the switch both my piggies spirits were raised immediately. Plus I find it much easier to clean my cage and keep it clean. I built my own C & C cage (6 feet long by 3 feet wide) for my two pigs, anticipating for my litter to be. I then went out and bought 5 fleece, all with cute patterns, and volaa, now I can just keep rotating them out every week, washing them with vinegar (I have read that this is safe for pigs) and drying with no dryer sheets (chemicals unsafe for pigs). I can see poops easier which I clear away daily, because Guinea Pigs, pregnant or not thrive in a cleaner environment, despite being quite messy.
Make sure she isn't stressed out. Try not to pick her up or chase her around, it can cause problems with the pregnancy and can lead to lethal side effects for your pig and her pups. This also means her cage mate. So far, my two get along just fine. They have small tiffs, but no one bites, chases, or otherwise "stresses" the other out. They simply express annoyance and the other backs off. So for now I have allowed them to live together as I see no reason to separate. I would make sure you have two females, because pet stores often don't bother to sex their animals. They lie to owners to sell them whatever they are looking for, male or female. I worked at one for a while and I was always very upset with the way animals were handled by so called professionals. However, to sex a pig yourself is quite easy. Just gently and slowly lift them up on their hind legs (your hand scooping their midsection carefully) and scoop their butt up in your other hand to tilt them back into your stomach (I do this on a bed or counter, so I dont have to bend much to line my pig up to my chest or stomach for support. Remember, they have about twice as many bones as you and they are quiet fragile! They appreciate a slow and gentle hand.) Once you can peek you will see the Y shape. If it is just a Y its a female, however if there is a dot in wine glass Y then you've got yourself a boy. I am sure you may have known this or been told this, but just to be sure, it is something to check. If its is a boy, you will need to remove him from her presence because he can injure her and the babies while attempting to mount her. Again, I have a male and female. They came together and I was told they were both male. I took them to the vet the same day to ensure I knew what I had and surprise. I neutered my boy a month ago and now they live together happily and he doesn't try to do anything except groom and cuddle her. If I have little boys I'll have to separate them from their mom and sisters by 2 weeks, or I could have more on the way again!
You can find a lot of this information researching as well
make sure you cross reference and make sure you know who you are getting your information from
Best of luck!!
