Is it normal for my mother to keep adopting children?

Alright so my mother decided to adopt 4 children a few years ago. Out of the 4, 3 are blood related and under the age of 10 (theyre 7, 8, and 9). The other one is 14 years old now but we have had him since he was about 12. Anyways now she wants to adopt the three siblings of the 14 year old. These siblings ages 11, 4, and a 1 year old stayed with their birth mother by choice.

Now the mother has lost her children again and they are asking my mother if she would like to adopt if it was possible. My mother was glad to be out of the foster care system so it confuses me that she says if it is an option she would like to re obtain her foster parent license and eventually adopt the three children.

I am drained just to hear that. I'm a young adult of 18 and I love the kids I have in my home now. However, that would make seven kids and I think it is too much and not fair either. Am I being selfish? Is it normal for my mother to keep adopting? I feel like she doesn't care about what her REAL kid wants.