Joy: Okay, well being that she is pregnant and will not have too much of a need to be on it as she'll be happy to spend some down time. I have never heard of the PVC, that seems a bit silly to me though, that seems like a crude splint that is not fitted for a pig leg. Pics would help but knowing her status is good enough for now. The location of the break, if indeed it is a break is a bit difficult to say what methods will be best. It could be a foot break, a hock break, a stifle break, etc. Is it fairly swollen and very sensitive to the touch? I'm assuming if you're guessing it 'might' be broken that there is no deformity?
Your best bet is probably a soft cast. Straighten the leg out, but keep a slight bend in the joints so that if she bumps it it will have give, this applies if the break is the in the joint as well. Splinting it completely straight will lock the joint up for good. Next apply a heavy cotton gauze, castign gauze is great, they come in big rolls at the pharmacy, some dollar stores have them too. Wrap firmly in gauze, and make sure if there is a break it is on good enough to stabilize it. Then use vet wrap and firmly (not too tight) wrap the leg, securing the gauze, start at the top and work your way down. Completely cover any exposed gauze, the very top and very bottom are acceptable to have a bit of white showing. This is inexpensive and effective. This will do well if it a simple fracture, or a complete break, provided it is not a compound fracture or has more then one, or two breaks. If you feel she needs added stabilitzation you can make a splint. Thick wooden dowels, or heavy guage wire, like the made cattle guards out of and be bent to shape around the limb for added support. Make sure to tape any sharp ends. Soft casting will probably be sufficient in your case. You can also purchase casting material, your vet should sell it to you, that is a fiber glass resin you soak and apply. Do you soft casting with the gauze (no vet wrap) and apply your hard setting cast on top of that, make sure to smooth it out and make sure there are no air pockets or gaps in the seams.
Again soft casting it probably your best bet with her at this time. It may not neccesarily be broken and this casting will work well if it is or if it is not. It's economical as well. You sound like me, in terms of giving everything a chance and going to lengths for your animals. Bless you. I wish the best for you and momma pig. Please don't hesitate to post or PM me if you have any questions.
Also one last note, watch the antibiotics. If she does not have any open wounds, and the limb is not grotesquely swollen you will probably be alright to wait on antibiotics as she is pregnant and close to term. Antibiotics are more of a hinderance then a help. Just be careful, if you do, do minimum dose. I would wait to vaccinate until after piglets are on the ground, read the directions,and ask your vet first. Take care.