You should be happy that your daughter WANTS to bring her friends to her house. This says that she is comfortable in her own home as well.
So what if 2 of the girls are wealthy and have cleaning ladies.. That has nothing to do with you and your home.
Of course let them come over. Why not? If you choose not to open your home and yourself to her friends, then your daughter will be sleeping over at her friend's houses and when that happens, you won't know what they are doing.
I LOVED it when the girls stayed at my house. I had the go to house and they had the entire upstairs to themselves. Do NOT just retreat to your room and let them go. It is imperative that you do periodically check on them to make sure they are not doing something stupid. I caught 1 girl disabling a window alarm and she was actually going to try to sneak out by using a sheet from the 2nf floor which could have been a disaster. So always be aware of what they are doing in parental mode... not friend mode.
As for food, pizza is good. Have some snacks, drinks, let them know the house rules. Most of the girls who stayed here slept in until their parents picked them up around 10. I always had cereal and bought donuts a lot as well. It was common for our house to have a house full of girls on Friday and Saturday night.
This is a critical age where it is important for you to be in touch with what is going on in your 13 yr old's life. Keep your communication lines open, let them sleepover and have fun.