I struggle with this.
My sister frequently asks me to "borrow" money, which she pays back about 50% of the time (max). I'm not massively well off, but have a career/salary (part time senior school teacher type salary) husband who also earns (more junior teacher). DSis is a single mum and works in a zero-hours-contract type job.
At the moment, she owes me several hundred pounds from Christmas. I just don't mention it (I never do). I only "lend" her money which won't absolutely break us (so I can still pay the bills/get stuff for the kids). But I wonder whether I should actually bring it up/ask her, so she can't stick her head in the sand (I think she kids herself that she pays me back, and deliberately forgets the many times she doesn't). But she probably won't have the money to give me, and it will just make her feel shit about herself.
I feel like I should share willingly with her - she's in a much tougher position than I am, because I've been lucky (and worked hard - but the ability to work hard is also luck, right?). But when I realise she's highlighted her hair, or her kids have iPhones (mine don't), I feel resentful.
I'm not even sure what my question is. Do other people "share" with their siblings willingly in this type of situation?