Learned everything I know from Youtube and the Internet... need some confirmation!

Hi and welcome to the forum! She should see a vet for the eye, it sounds painful if she's keeping it partially shut (piggies are prey animals and hide their illnesses), and if infected and untreated she may lose sight in it. For anything else she would need to see an exotics vet but any vet should be able to treat her eye. If you take her to a small animal vet, which means cat & dog, I suggest printing the dangerous medications list from www.guinealynx.com to make sure they don't prescribe anything that would harm her. Personally I would find an exotics vet so she can have a health check along with her eye being treated. Guinea pigs are herd animals and are much happier with a friend. There's no way that I'm aware of to predict how big she will be.

If you get a piggy in the future, consider adoption. Pet store pigs are often sick or pregnant.

To answer a few of your questions...

She will live without a friend, but cavies do SO much better with a buddy. They often get used to humans and less skittish, and much happier, with a friend.

I have no idea how to measure a pig, or to predict size later in life.

In order of best to worst, CareFresh, Aspen, Kiln-Dried Pine. (But don't worry, all are good choices. CF is just easier on the feet, and aspen a teensy bit healthier.) Fleece is also a great choice, but is in a whole 'nother category of bedding. Only use it if you can spot clean once a day, and wash weekly. I use fleece like many others here, and it's a VEEEERRRRRY cost-effective solution. However, fleece in a pet store sized cage (which a guinea pig shouldn't live in anyway) is an absolute nightmare, as all the poo and urine is concentrated to one area. Using bedding or fleece really depends on you and your situation. Try it out and see if it'll work!

If you have any questions about food, care, cage size, or anything at all, don't hesitiate to ask

As it turns out, an exotic pet vet is literally a minute away! I'll look into that Friday if it's still bothering her. Have you ever used the Pine Bedding from Rural King? It says that it's kiln dried, but you can never be too sure! I get a HUGE bag of it for only 5 dollars; I filled up my whole cage and it only made a dent in the bag! A C&C cage that is 2x4 grids can fit two piggies right? I may be persuaded to get her an abysinnian friend if all goes well. Is there anything I should be concerned about with having two piggies instead of one? Are there any differences between Abyssinian and American piggies? What are the best veggies to feed daily? Last of all; is it true you can potty train the pigs? Thanks!

A 2x4 will work fine.
The only thing is you may need to buy a tiny bit more food/veggies/hay, but not much.
Abyssinians tend to be more mischievous (but that's anecdotal, not scientifically proven) and I can confirm that with mine. She is a tiny little troublemaker! But I love her.
Some good veggies are lettuce (red leaf, great leaf, or romaine), and bell pepper. You can give others as well, but those are the staples.
You can kind of potty train, but don't expect them to be fully litter trained EVER. If you put their hay where their litter box is, you can catch 60-75% of their business sometimes. But for dome pigs, it just doesn't work.

Okay, so does this sound ok?... I have a 2x4 C&C cage with kiln dried Pine, complete with 3 levels (a bi level on the first grid and another completely different 2nd). She has a 32 ounce water bottle with access to it all day, an all day hay holder, and 1 hideout on each level. As for food; I fill her bowl about 1/4 the way up with pellets in the morning, and in the afternoon a cup of vegetables that include romain lettuce, green pepper and a few leaves of baby spinach (I know they shouldn't be fed that too often). Also, do I need to buy a new water bottle if I get a new pig?

The cage idea sounds great! I'm not too sure about the water bottle. I have one and my two share fine.

One tiny flaw in your plan. Piggies should only have 1/8 cup of pellets daily, not a quarter of a bowlful. I give my pigs half their pellets and half their veggies in the morning, then repeat in the evening.

I just remembered something that may put a roadblock in my plan; is it true you have to wait at least 2 weeks to introduce another piggy?

Yes, for quarantine purposes. You can keep him/her in a small cage for that time, but keep them in separate rooms to prevent airborne illnesses from spreading.

This is also true with my little Abyssinian, Miss Rhino! What a little bag of mischief that piggy is! Honestly, she instigates at least 75% of the squabbles and then wins them to boot. But, just like Kenna, I couldn't live without her.

Abyssinians tend to be more mischievous (but that's anecdotal, not scientifically proven) and I can confirm that with mine. She is a tiny little troublemaker! But I love her.

Click to expand...

The recommended time for new piggie quarantine is 3 weeks.

Also, what is the best way to handle a skittish Guinea Pig? She bit me and drew blood the first time I held her! Now she doesn't bite hard, but she still licks and nibbles at my fingers. She will also seek out my fingers to nibble on them! I try to hold her everyday, but she still doesn't trust me (though, I've only had her for a week). Is it because she's young? The pet store employee said that this would be her first direct human interaction she's ever had.

If the pig is only 3 months old pellets do not need to be limited to 1/8 c. Likely, if the pig is from a pet store she's pretty young. Guinea pigs can not be potty trained. They tend to go in the same areas, but they will go when they need to go wherever they are. If her eye is crusty and partly shut she needs to see a vet.

ETA: Guinea pigs tend to be skittish their whole lives. Mine hate to be held, so I don't hold them. However, guinea pigs don't usually bite and biting and acting uncomfortable when being held can be a sign of mites. If she came from a pet store mites are a high possibility.

I'll just leave these links here as you might find them helpful

https://www.cavyspirit.com/sociallife.htm#Quarantine
https://www.cavyspirit.com/sociallife.htm#Introductions
https://www.guinealynx.info/handling.html
https://www.guinealynx.info/diet.html

As for the biting does she have any signs of hair loss or itching?

Thiers also a link on nutrition and diet if your still trying to find some staple veggies for them .I've also used pine then switched to aspen as it was much more inexpensive.but altimatly I've went to fleece now.what I do for mine as I know they like to nip me is just let them sniff and lick my knuckle of my finger so if they do nip it dosent hurt .