You can certainly apply for GCMS notes, but I doubt it will reveal anything new.
Your sister and BIL were granted TRVs on the grounds that they need to return home to your niece + your BIL's mom (family ties to India). With your niece applying as well, their family ties to India have reduced significantly + they did not prove your BIL's mom's dependence on your sister and BIL. This explains the family ties refusal reason.
Also, I suspect the visa officer is not convinced that she/your sister and BIL want to spend significant money to visit for just 12 days. That would explain the Purpose of Visit refusal reason.
If your niece reapplies, I suggest she must include:
1. A plan to visit during her school break (detailed day-by-day itinerary) + keep the visit to 3-4 weeks max.
2. School mark sheet + student ID + exams scheduled after the visit (even if it is 1-2 months after the visit) + any other event-related reason to return (for example, she is part of the school sports club and there's an event scheduled after her return)
3. Evidence of your sister's and BIL's strong ties to India (his employment letter and NOC + his mom) + their flight tickets (refundable/allows for date change). The idea is to prove that your sister and BIL must return to India = Your niece will return with them
4. Include a Travel History explanation (just one entry of course). Color scan the Australian visit visa + mention the purpose of visit, entry/exit dates
