Answer:
The reactions of Mrs. Frank and Mr. Van Daan was different because they were fighting with each other before the news broke. Mrs. Frank knew that someone was stealing the food, but at that moment she came to know that if was Mr. Van Daan. She lost her temper and told him to hit the road, even when she knew that whoever goes outside, will surely die.
When Miep comes and break the news of invasion, the whole group goes crazy and there is great rejoicing. It is described in the play:
"Dussel embraces Mrs Van Daan . Peter grabs the pan and parades around the room, beating onn it, singing Dutch National anthem. Anne and Margot follows him. Margot take the flowers from Meip and distribute them to everyone"
However, Mr. Van Daan is feeling guilty because of what he did. Seeing that, and due to the happiness of invasion, Mrs Frank successfully regains her composure and forgive him.
It is described in the play that:
" (Mr Van Daan, sitting on the couch, suddenly breaks into a convulsive sob)
Mr Van Daan: Please I's so ashamed
Mrs Frank: We've all done things we are ashamed of.
Mrs Frank: (through her sobs) When I think of the terrible things I've said........
Mr Van Daan: No! No! You were right!
Mrs. Frank: ....that I should speak that way to you! Our friends! Our guest! (she starts to cry again)"