No. Basically every boss will have a mechanic that will ignore taunt. Some more, some less, but no single boss will stay on the tank 100% of the time. That would be stupidly easy too since almost no attacks from dungeons bosses kill tanks (very few exceptions).

With the Lamia, best bet is to stay in the water where she doesn't get the shield, but the group can still hit her from the island, keep taunt, and wait. She will come back eventually.