My dog's brother died of jaundice. Is my other dog at risk too?

Jaundice is caused by so many internal issues, that it is impossible to tell you if this is a contagious thing or not. I would highly recommend discussing with the vet that treated her brother what condition he had and if it is contagious or not. Then you have to look and see if his issue was congenital (something he was born with). If it was, then her being a sibling does mean she may also carry the genetic defect to succumb to the disease as well unfortunately. However, you still need to know what the condition is specifically in order to know if there are any possible preventative measures you can take for Joplin.
Jaundice can be caused by a congenital liver defect, which is a long list of possibilities. Hopefully we can find out what the brother had soon. If that is not possible, then your next step should be to get Joplin a DNA test to find out what diseases she is susceptible to,. Ask your vet about this and they should be able to test her right away.
I hope that Joplin does well and continues to be a happy healthy puppy moving forward. Take care!