CBSE

She cannot take admission in B.A. Economics (Hons.). Without maths being one of her subjects in 12th in DU in spite of a good percentage.

There are chances that you might get admission.
Please check http://www.du.ac.in/du/index.php?page=cut-off-2017 for last year's cut-off of SRCC and Hindu.

Yes, with this score, you could get admission in any stream of B.Sc in St. Xavier's Mumbai. But, BA could be a slightly tough option. BMM & BMS are entrance based.

Hello Rohan, Yes, it's worth. If you thought that you have not score well according to your ability then you should try this. With the help of CBSE Improvement Exam, you stand a chance to give the best in the exam and prove your abilities. It will help you to get enough marks to get admission in NITs and IITs. But remember that the most prime and mandatory rule of CBSE Improvement Exam 2018 is that the student must have passed the Board Exam. The failed students would not be able to appear for the exam. You can get the complete details regarding the CBSE improvement exam from - https://scoop.eduncle.com/cbse-improvement-exam.

You can go for Bachelor of Arts, as it allows you to opt from a number of subjects. You can opt any subject of your choice.

If you think you can perform better, it is a good option. But, it depends on what course you are willing to opt.