7yo CANNOT STOP speaking for her sister, ideas?

My stepdaughters are 7 and 4, and 7 CANNOT STOP answering for her sister. It's constant. Some examples:-4 is giving me a picture she made at daycare and explaining what it is, 7 stands directly behind her and says, "She says it's a picture of an elephant." 4 can speak just fine, and no, that's definitely not what she said.-I asked 4 if she'd stepped outside yet to see if she needs a jacket. 7, yelling from a different room, "No, she hasn't!"-Ask 4 what she wants for dinner, 7 pipes up, "She wants macaroni and hot dogs."-Told 4 she can take a stuffed animal to daycare, and as she's picking which one she wants, 7 starts in with, "But can she take a blanket? What about a pillow? How many stuffed animals?"It's driving me crazy. In the whopping 2 hours between when they got home last night and 4's bedtime, 7 spoke on 4's behalf 17 times (mind you, 4 does not need anyone to speak for her, she can do that just fine, and 7 doing this is in no way an assistance. 4 was explaining Paw Patrol to me and 7 starts telling me "Oh, she actually means [completely different thing]", which is most certainly not what she meant). Verbally correcting 7 has made no difference at all, so I'm looking for ideas on discipline, because I don't want 4 to feel constantly invalidated. I had told 7 every time she does it she will have to pick up/clean up 10 of her sister's toys (like mega blocks, for example), which was such a non-deterrent she immediately spoke for her sister twice, then went and cleaned their room. Obviously that's not going to work. Compounding the issue is the fact that their bio-mom encourages 7 to be completely responsible for 4 at her house, which we've explained to 7 many times that she is not 4's mother, she's a kid and she is not responsible for her sister.Thoughts? Ideas? I can expound on anything if need be. via /r/Parenting https://ift.tt/2JY7S1b