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Can I say,

(a) She slipped and fell down at the bathroo.m

(b) She slipped and fell down on the floor (in the bathroom).
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(a) She slipped and fell down in the bathroom.
(b) She slipped and fell down on the floor (in the bathroom).
Comments  
Students: Are you brave enough to let our tutors analyse your pronunciation?
How about this:

c) She slipped in the bathroom and fell down.
Excellent!