@Teenyton
Stepmums, why don't you just suggest putting her under the stairs, Harry Potter style? After all, she's just half the time there. She's not a real person. Unbelievable...
I honestly just don't get this at all.
I am a stepmum and in OP's shoes, I would genuinely think the best thing for SD would be to have her own bedroom from the start, even if it's smaller?
I actually think OP is putting SD ahead of her own 2 girls here because her plan is that SD will have her own room always, and neither of them will. It's not ideal for a 7/8 year old to share with a young toddler either, but that's what OP is saying her DD can do, so that SD doesn't have to and she has her own space?
A lot of people would be saying SD has to share the bigger room with DD6 so that the new baby could have their own room when needed, so nobody's sleep is disturbed.
The option for SD to have a bigger bedroom solo is just not there, whichever girl sleeps in the bigger room will also need to share with the baby. It makes no sense for DS to be in the box room when there will be another, bigger room standing empty 50% of the time.
SD may say she's happy to share with the baby right now, but that's just because it's not reality. Will she really be happy in a year's time when the baby moves in, her room gets filled with baby stuff, she can no longer use it after baby's bedtime and she's potentially being woken multiple times a night?
I understand that she feels upset about it right now but, thinking of my own SCs, one of whom is 11, I think a sit down and proper chat about the reasons why could make her see it quite differently. I know my SS would feel happy if he thought about it in the sense that he might have a smaller room but it would be all his own while his siblings had to share.