Hi Misfitless
thanks, your questions are very reasonable and already show insight into the situation.
So...DC1 was initially THRILLED at the news we were going to adopt. Then came a long wait (several years) and then then pretty sudden news (2-3 months) notice that it was all going to happen. During this time DC1 developed a really idealized picture of how perfect and great everything would be with a baby. She is great with our friends' younger children, in doses of a couple hours and they really respond to her (she has even been paid a nominal amount to help at a 4 year old's birthday). So she imagined herself as the perfect big sister of a perfectly behaved and fun little sibling.
The reality of all children of course is more varied, and while DC2 completely admires and idolizes DC2, DC2 was disappointed that often DC1 prefers to be comforted by her parents, trusts us more, and has developed some (healthy) sibling rivalry of her own for our affection. In other words, DC1 was a bit disappointed in the reality. She had not anticipated (despite our discussions) how demanding a young child can be, and that young children's needs can be very immediate (safety, food, etc.)
Let see, DC1 was quite involved in the adoption process -- not the paperwork of course, but talking about it, planning the trip, and yes, we all traveled together. DC1 got sick on the trip (fever) and thus it was less fun also than she had hoped as a result.
I think you are right that this all happened quickly in DC1's experience. It seemed abrupt, and there is no turning back!
Also, none of her close friends have siblings, and all have dogs (not an option for us due to work/travel), so she feels hard done by there as well!
We do try to spend time alone with DC1 each day and more at the weekend. One of us spends about an hour most nights at bedtime (reading together mostly) which almost equals the bedtime routine for the baby!
It does feel that she needs an excessive amount of reassurance that she is still central to us...nothing fills up this need.
My mum said something very insightful even before we brought DC2 home, re new siblings, which was to imagine your partner announced he/she was bringing home a new spouse and that he/she was sure the whole family would all love this person and it didn't mean he/she loved you any less. While this may be insightful, it doesn't help me to know how to solve it!
On a positive note, I know that the two children love each other, and are really happy when they are getting along well and unhappy/sad when they are not.
So, how did you handle it in your situation? We have been very accepting of her atypical behavior, during the transition, but she is becoming nastier to others (including potential friends) as her self-centered behavior is tolerated. I want to reassure her of our love but not accept taunting, being rude, and literally exploding when reminded to do things like clean her teeth, quickly followed up by "you don't love me!" even when this is completely illogical in the situation.