I have students with only 1 month to prepare and although such a short time is never considered optimal it can be done.
with a 25 in verbal it is clear that there are some fundamental skills that need to be worked on as well as some fundamental misunderstandings going on.
have you ever tried diagramming sentences? just as in math where there is a clear order of operations ( parentheses, exponents, mult/div, add/sub) the same idea can be applied to sentence correction: core sentence, main clause, subordinate clauses, subordinate subordinate clause etc. there is a priority of information that you need to be very clear about.
if this sounds like it could apply to you let me know and I will elaborate.