How to ensure new cat feels safe

How to ensure new kitty feels safe after old cat spent her last days in distress

Hi guys. My sweet girl passed away last week after being diagnosed with a genetic condition that causes chyle build up in her lungs. That being said, her last day she was uncomfortable after returning from the ER vet (I had her regular vet put her down so I could have time to say goodbye). And had been distressed to a degree (not a lot, even the vet was shocked by her diagnosis) but still stressed.

How do I ensure once I get a new cat that it will feel safe?

Will it smell her distress? is there a way I can clean to prevent this? Thank you.