Hello!
The Dream debuff causes the target to enter the debuff status for two rounds, but cannot normally be applied to a ninja that is immune. Under normal conditions, Kushina should break Dream status once her immunity returns at the end of a round (assuming that her immunity suppression ends at the end of the round), but there is currently a bug that sometimes allows the dream debuff to supplant the immunity, allowing this to take priority, resulting in Kushina to remain debuffed for the full length of the Dream effect.

As for Illusion:Mirroring Vision, the normal rules for removing Dream apply. Once chakra is at 30 points or higher, Dream can be removed with no penalty.
Thank you, and if you have any more questions, feel free to ask!