By default bsc maths or bsc physics is difficult for both boys and girls as syllabus for boys aswell as girls is same. BSc maths or BSc physics or BSc statistics is by far difficult than the toughest stream of engineering or btech or bsc chemistry. BSc/BS physics or maths or stats are much abstract and mathematical when compared to any engineering field or any bsc field.  I had many friends in bsc dropping out of btech after 2 years of engineering maths and joining BSc pcm and literally begging our teachers and principal to change stream or atleast replace maths and physics with some other subjects in first year itself. So majoring in maths or physics in final year of bsc is way more difficult than the first year maths and physics subjects of BSc. But if you sincerely attend all lectures and get your concepts cleared on time then it won't be so difficult.

There isn't any difference for girls or boys because courses will be same for both. Typically BSc does not considered is very tough even in mathematics because we have engineering courses too.

if you regularly follow the classes and practice the problems then BSc in mathematics would not be tough for you.the syllabus generally extends the topic whatever a student read at school level and proper strategy with regular prepare this will give you more than average score.