she will need attractive (to her) nesting materials. Some species of bombus
seek out old mouse nests in which to start their own nests. This might be a
good start. You could experimentally add a few very young or emerging
honeybees. It is possible that they might forage and thus enable the bombus
to expand her brood nest faster than if left to herself.
Today I saw some bumble bees seeking nest sites. I might try this myself.
Chris Slade