There are generally two kinds of account sharing, those that may share access with their siblings, spouse, etc… due to circumstance or because they are generally unaware of the policy and those that share to gain advantage (i.e. power leveling, etc… ).
The latter can be damaging to the gaming environment, which is what we tend to focus on. We generally understand how it happens with the former, which tends to be less damaging overall, but can cause serious security risks for the account.
I can’t make any guarantees, Who, but our staff encounters many different situations around this. They can definitely look into it and make accommodations if at all possible. If the siblings have same last name that would definitely be a help, not to mention if she is still in contact with her brother, just in case there are questions.