I don't wear make up. I think the last time was for a wedding in 2014 & that was only a bit, to avoid the hassle with my Mum. (A bit of mascara & lippy in exchange for a nag free day seemed like a fair trade).
So, I had no idea how much it cost, google tells me around £15 for a MAC lipstick. That's not expensive, I was expecting it to be about £40 from the comments on here.
I don't like young girls wearing makeup, thankfully the 12yo isn't remotely interested, she's all about the Slime. (Which is costing me more than MAC makeup 😂). I would have allowed her make up at 9 if she'd wanted to play/practice/have fun with it, but she would have had to clean it off properly & she wouldn't have been allowed to wear it out of the house. No skin covering stuff like foundation etc either.
I like buying them things they really, really, really want, so in your situation I'd try to buy something else that she really wants instead, but if there's nothing she wants more then I guess, for me, it would depend how her (your) parents feel about it. If they're fine with it, then I'd buy it for her. But I'd buy her exactly what she wants and that MAC, not another brand. Unless you give her the option if 1xMAC or 2x a cheaper brand.