Thank you for choosing Doctor Spring. Chances of pregnancy are nil in your girlfriend's case, because intercourse happened on the 4th and 5th day of her menstrual cycle. Chances of pregnancy are bright, if intercourse happens between 12-16th day of the menstrual cycle(in a 28 day cycle) in a female who has regular periods.
Sexual intercourse immediately after completion of period can cause some amount of bleeding. This can happen due to tender uterine lining, which happens due to shedding of the endometrium.
Brown bloody discharge is nothing but left over blood after a period. Chances of pregnancy are absolutely nil.
Vaginal irritation alone does not suggest anything serious. In most cases it resolves spontaneously. But if it does not then it could be due to reasons like use of tampoons/ lubricants/ poor hygeine/STD/ douches/ yeast infections etc.
Here are my recommendations:
1. She should avoid using douches, perfumed toilet tissue papers, avoid bubble baths and make sure the area is dry and clean.
2. In case she continues to have itching or develops any other symptoms like discharge, rash, burning urination, ulcers etc, she would require to see a OBGYN for examination, swabs(discharge) from the vagina to know the casuative organism and urine examination.
3. She can wait until a week for the bleeding to stop, but if she continues to bleed further she would need to get in touch with a OBGYN for examination.
Hope this helps.