What a great idea to do the x-ray! Now you can set your mind at rest. I know it's easy to worry about her, given her genetic issues, but lethal whites are unfortunately doomed to die due to their genetic condition, and usually it is sooner than a normal healthy pig. So instead of worrying about whether she's about to die, or if there's some undetectable issue manifesting, maybe try to accept that her life will be a bit shorter than your other guinea pigs, and focus on giving her the best quality of life you can and appreciating the moments you have with her (and I know you do!). There's that old saying, quality beats quantity
