How much would you loan to a family member?

For context, I just started working this year.

My sister has asked for a loan on numerous occasions. At first, the sums were small ($50-$100) and recently, she asked for a loan of mid 3 digit sum. At first, I did not want to lend her the money but I thought she is family and if not her, who would loan her. I rather she loaned from me vs an outsider. She has been paying all her loans to me so far but it got me wondering...

When should the line be drawn? When do I decide to really say no, even if it is a close family member? Do I lend her as long as she pays back and if not, what is the amount that I should stop?