Okay I like you have 7 and have had this exact issue with all of them, and we are a brady bunch also (have had his since itty-bitty's) and am currently in the same position with my just turned 4 year old DD and my 21 month old son, my DD loves to take it from my son (I don't break until about 2 year old) although she is fine having a cup and uses them all the time. I notive for my DD it is a comfort thing, if I am busy with the baby, or just don't have enough hours in the day, she wants one. I have just let her have it, she get's one and has learned to pick when she gets it...know. In the beginning I would give in also, just so the baby can get to sleep, but slowly cut it off, I did the same with her older brother who is 6 know (he hasn't wanted or asked in years) for me and my kids the more forbidden I made something the worse it got, so I would compromise. Watch your DD she has a trigger and then find the middle ground. It doesn't have to be all or nothing. And a little peace and harmony is not a bad thing. Your little girl is still a baby herself and she see's all the attention the baby gets, and how much comfort the new little one gets from it, so her reaction is normal. I don't know if this helped any but good luck!!!