Problems with MIL

Hi everyone my bf and I have a 10 year old daughter we live with his family, which are 3 more kids (11, 7, 6) 2 girls one boy and for a few times my MIL will leave my daughter out. She’ll go shopping or buy food and come back only for the two younger girls. I’ve expressed my frustration with my partner and he says he will speak to her. He hasn’t. Yesterday, again, she went out to the store and came back with goodies my daughter asked “do I get any?” She replied “no I only bought two for the girls”

My daughter just told me this morning and I’m so upset because how do you explain to your daughter that this isn’t right but also not have her feel some type of way by noticing??? I text my MIL (first time ever) saying next time can she let me know and I’ll happily send her money to include our daughter. She hasn’t responded.

How would you feel??? How would you feel about this?