Pregnancy after stillborn...?

I'm not sure how it works but my sister had a still born a few months ago at around 26 weeks or so,again they didn't know how or what happened but she thought it was to do with some paint used at a factory.She's been trying since then to no luck but she's looked everything up and shouldn't have any problems conceiving and that a stillborn is VERY rare to happen again.But when you do conceive the doctor will make sure they keep a close eye on you more than that time..So sorry what happened to you.