Relative Clauses

Mathematics is a subject (that) she has little interest in. (這句子是正確的)

Collocation (搭配) of the noun "interest":
to feel/have/show/express (an) interest "in" something

關係從句的標準句法:
Mathematics is a subject in which she has little interest.

Main clause 主句 = Mathematics is a subject
Dependent clause 子句 = she has little interest in Mathematics (a subject)

"That" can be used instead of "which" in the relative clause, but it is not used immediately after a preposition. The preposition has to put at the end of the relative clause.

"That" can also be omitted in the relative clause if it represents the object of the clause.

I know it's weird but it's about proof reading and mc questions in the exam.:(

2014-06-08 15:56:28 補充：
But thxxx anyway:P

Normally, the following simple sentence should sufficiently express the meaning:
She has little interest in Mathematics.

One can emphasize on "Mathematics" by using expletive construction:
It is Mathematics (that) she has little interest in.

2014-06-07 07:03:16 補充：
One can respond to the question,
"which subject she has little (or the least) interest in?" by saying:

Mathematics is the subject (that) she has little (or the least) interest in.

(Note that "the" is used instead of "a")

2014-06-07 08:30:09 補充：
Sorry, asking a question by

Which subject do you like most?
Which subject does she like least?
Which subject does she have little interest in? (a bit clumsy...)