This is what I would do:
Leash Bella when you know someone is coming over. Have the company come in and completely ignore her until they are in and settled. Allow Bella to go over and sniff/say hello. If she tries to jump tell her no and put her in a sit/stay and when she does, give her a treat. Repeat as many times as necessary and it will work. The most important thing though is to make sure everybody ignores her until she displays the behavior you want ie: sitting calmly and waiting for you command that she can say hello.