It is a HUGE plus that the male is the bigger dog and the snotty one is a small female. But Dachshunds get themselves SEVERELY injured and even killed behaving like this toward bigger dogs. It is all too common.
Don't leave them alone together at all. A leash--attached to a harness rather than a collar because of Dachshund spinal issues--on the Dachshund that you hold while supervising could be just the thing.
Dachshunds were bred to hunt badgers underground. Badgers are very aggressive, and the Dachshunds strongly tend to win these battles! They have powerful jaws and tend to lack wisdom in choosing to take on other dogs. So don't let the Dachshund treat the Mastiff that way. Separate whenever you can't supervise. A baby-gated or exercise-penned area would be better than crating the Dachshund. She needs to move around.
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Kathy Diamond Davis, author, "Therapy Dogs: Training Your Dog to Reach Others," 2nd edition, and the free Canine Behavior Series articles at http://www.veterinarypartner.com/Content.plx?P=SRC&S=1&SourceID=47