Missing out

So I baby sit my niece and I get paid 100$ a week. My sister just told me today she can’t pay me this week so I’m a little annoyed because it’s not much and she goes out and spends money on tattoos and stuff. Her and my nieces father aren’t even together and she just paid for his eye appointment yesterday... they both work full time and neither of them can pay me this week? I have a feeling that she’s just going to screw me over because she’s done it before. This is all I get for income and I feel like it’s not fair that they are doing this.. eventually she just stops paying me and then quits her job because she doesn’t think I deserve to be paid and then everyone blames me for her loosing her job