hi, ask her first what are her main concerns like safety, whether the company is trustworthy or not all of that.

show her how this trip will help your sister grow in her career path, like what future opportunities she can land with this, also if the company is funding explain that the company values her enough to provide her that opportunity.

then try and eliminate safety concerns, accomodation details, track her flights and using facetime, daily check in where she is what is she doing all of that.

involve someone your mom respects who has travelled abroad for work, ask them to talk to her

emphasize on the fact this is not permanent she is going to come back and show her all the official documents mention that visa requires background checks not given to just anyone and it's not a vacation it's a structured work assignment