Hi- Wow, those are some gnarly nails alright! From the look of them (although the picture is sort of blurry) they could be cut even shorter. In any case that isn't likely to be the reason she can't bear much weight on her foot.
Sometimes they get a horny-type thing that grows off the side of the foot. It is usually on the outside edge and is some sort of spur that can be clipped off with nail clippers. I don't see that on her, and again, it wouldn't keep her from bearing weight.
Guinea pigs sometimes get an infection called bumblefoot, (ulcerative
pododermatitis) usually in a front foot. The picture below is what it
can look like. That is a particularly bad case of it. It is pretty hard to get rid of but it can be done. It
is usually caused by an injury where the skin is broken and germs get
in and make a swelling. If this is the case you can try treating it by
soaking the foot in warm (not hot) water/ betadine (you can get it at a
pharmacy or evenWalmart) solution, 2-4 times a day. Keeping it clean
and dry is very important. Some people wrap the foot
with vet tape but the pigs don't usually like it and take it off
quickly so it seems like a waste to me. It is better to keep the cage
very clean while waiting for it to heal. If this is bumblefoot, it will
take 2-3 weeks to heal completely. Keep up the soaks until the wound
closes and then you can discontinue them. Make sure there is no
infection under the scab though, or it will continue to grow and find a
new way out. Do keep the cage scrupulously clean until it is better. You should likely clean it daily or every two days at minimum. If
you don't see improvement within a week or so, you might have to take
him to a vet for antibiotics or other treatment, but I'm with you, it
is often traumatic for these little guys to go to the vet. If you can
treat him at home I'm sure he would appreciate it.
There is also a topical medication that some people swear by but I've never tried called Blu Kote. I think it is a medication commonly used for wounds in horses.
If it is a true injury ie. something is broken, she will heal over time on her own and probably be fine. Once the foot heals you should probably work on getting her some more exercise to get her weight down because being overweight will reduce her life span significantly. Make sure she gets play time on the floor or untreated grass at least 3 times a week. You can put her water and food at opposite ends of the cage to make her work a bit more for it. If her cage is large enough, try putting a board or brick in there for her to climb up on. If she has to climb over it to get to her food and water that's even better. good luck with her. I hope she feels better soon.
