Im sorry for your loss.
I think you're getting a hard time OP. I say this as someone who was left £0 from father and his stepson given everything. He changed his will when he met his third wife to exclude his two small children and add in his wife's child.
I never fought, I never argued, I never asked and I knew it would never be offered. My father was very abusive and despite spending his whole life telling everyone he treats all the child re the same, the fact the he chose to cut out a small child who he knew was already living in poverty in favour of his new wife's child is what hurts. It doesn't matter if it was 50p or 50k. It's the emotional hurt an action like that causes.
It's clear to me that you're upset your sister was excluded and it sounds like at a time you were grieving you wanted to make it better and offered half of your share. It sounds to me like you're hurt that your siblings aren't upset she was excluded and have not offered to make things fair by spilling everything four ways.
I agree that her income shouldn't be relevant but it's really hard not take it into account with the state if the economy and costs if everything at the moment. I don't think you deserve the hard time you're getting for having second thoughts about not giving her half and I also think you have every right to have hoped your siblings include her but now they aren't and it's clear you're going to be leaving yourself with less than you should have had to make up for your fathers decision.
You sister must be hurt, and I imagine like me, it's bjt the amount of money, it's seeing that at least two of her siblings l know full well she should have been given a quarter and they seem ok with her not getting that. I can see why you feel disgruntled with them too.
You can't fix or maintain her relationship with your other siblings. You can only focus on yours with her and yours with them but you could mention to them you're giving her a share and maybe they'll think again themselves. If you were my sister I'd be ok with you not giving me half because I'd know it's unfair and also not what your dad wanted.
Let's say it's £100, You could mention to them you will be giving her a £25 of yours and if they both did the same you'd all have what should have rightfully been done in the first place and end up with £75 each. Maybe they'll see how crap it first one person to have the guilt and lose out in order to make it a little bit fairer for the one who has been excluded totally.