Here is the original item:
Mackenzie had to leave the room,
(A) for her
father was noisily crunching raw radishes,
(B) which
produced so annoying a sound
(C) that
studying was impossible.
You wanted to do this:
McKenzie had to leave the room. Because her
father was noisily crunching raw radishes,
which produced so annoying a sound that studying was impossible.
Adding a period after room makes a fragment. Because her father was noisily crunching ... begins a subordinate clause. Remember that a subordinate clause cannot stand alone as a complete sentence.
You might want to review the rules.