This is the problem when 11 year olds make all the arrangements for social events. We don't know what the girls said to her or what she agreed to, or what she just assumed because someone said, "Oh, my little brother wants to see that movie too."
The thing to do is to get the addresses and send invitations. Indicate a drop off and pick up time at the theater or mall and a specific location, OR have the invited girls dropped off at your house for you to drive them to the event. Then you can either take them home or the parents can pick up at your house at a pre-arranged time. You can even say something emphatic but I would indicate what movie you've chosen and its rating, and add that YOU will be sitting with (or near) them and supervising at all times.
You could send an email but don't send an e-vite because usually that gives the recipient a chance to say "how many" are coming, and they could answer "5"! So if you send an email, it should be directly to the parent and say that "Susie is turning 11 and wants to invite Sally to come to ABC movie on (date and time and location). I will be sitting with or near them, and then will take them to XYZ mall for pizza afterwards. You are welcome to drop Sally off at my house at (address) at (time) for me to drive her, or you can drop her off at the theater entrance at (time). My cell number is xxx. Please RSVP by (date) and let me know if there are any food allergies I need to be aware of. I will drop her at your home at (time) or you may pick up at (location, time) if that's more convenient for you. Hope she can come!"
I don't know why people get the idea that they and their other kids are included - maybe it comes from all the big venue parties at bouncy houses when the kids are 3, and all the parents hang around with the other kids because the supervision is needed. Then it extends to older kids? I figure, if your kids are old enough to be left without you in school, they can be left without you for 3 hours at a party.