A: Rita's sneezing again.
B: Yes, she _________ a terrible cold.
(must have / must be having / must have had)
My answer for this is: Yes, she "must have" a terrible cold.
In my opinion, "must be having" shouldn't be used here because "having" in this sentence is a stative verb/non-action verb and it has no continuous (progressive) form.
On the other hand, "must have had" is in Present Perfect Tense and can't be used here because it'll imply that the action begun in the past that has already been completed.
The thing that makes me confused is the adverb "again." I hope someone can help me with my sentence. Thanks a lot!