First of all, after 4 pregnancy tests coming out negative, it would make sense that she is likely not pregnant since one of them alone is usually 97% accurate, let alone 4 of them.
However, one thing sticks in my mind here and it's one that perhaps, should be discussed with her doc. The pregnancy tests are coming back negative which means that there likely isn't an active pregnancy going on there BUT, the symptoms she has described can also be symptoms of an ectopic pregnancy (one that is in the fallopian tube rather than the uterus). The shoulder pain, the abdominal pain etc., can be signs of an ectopic pregancy. Of course, they can also be symptoms of a digestive problem such as constipation and she may simply be late due to worry (which is evident by the Plan B option and then, the 4 pregnancy tests
I say that if she feels worse, she should be seen by a doctor to see what is causing the discomfort as it could be gastrointestinal rather than gynecological. I also say that she needs to relax and just let her period come. It's like a pot that won't boil while you watch it....walk away and it'll boil!
stress can throw off periods!
Let us know how she's doing. I highly doubt given all that you've both done that she is pregnant. But, ya might wanna check into some other methods of birth control other than just condoms since they can break or at least switch to a different brand and make sure that they are fitted properly. If she doesn't want to go to birth control pills, she can also insert some spermicidal foam (over the counter in any drugstore or Walmart) so that if the condom does break again, there is added insurance there if you know what I mean.
Let us know! I'm sure she'll be ok!