Favoring child by her newest boyfriend

I’m thinking about stopping my friendship with my friend of 15 years. She has two children by her ex, and one by her current boyfriend. She treats the other children like shit. Won’t buy them new clothes, toys, if they ask for something it’s an immediate NO! The youngest gets everything. I believe she does this because she’s with him and wants to prove she’s worth being with by the way she treats their child together. She’s told me before she hates her first kids father because he’s a bum, so I’m thinking she’s holding some resentment to her first two children. Either way it’s not right. I said something to her about this and she told me to mind my business. So I feel it’s only right to cut off ties with her. She’s a fucking LOSER for this!