demotion - promotion
DD1 needs to feel that she is still number one, however deluded that might be,
Make sure anyone arriving at the house greets her first, talks to her ask what she has been doing, supply visitors with little gifts, to be given to her, " I hear you have become a big sister", give her time and attention, make her feel important.
Then ask to see "HER" twins(brothers/sisters?)
when referring to the babies, try to phrase it so she has ownership, "this is DD1's little sister", "can you show X(visitor) your little brother"
it really makes a difference, they resent the "attention seeking intruders" less when they become "their" infiltrators.
Involve her as much as possible, ask her what she thinks when the babies cry, "what do you think your brother/sister needs?" "shall we change your brother nappy?", " shall we feed YOUR baby sister".
If anyone is visiting, get them to watch the twins for a short time, even if you just walk up the garden on your own with DD, and pick some flowers, she will really appreciate a few seconds of one to one, they find it reassuring.
If you can get her to start to think of them as hers and the role of BIG sister an important one, you will have a much easier time years to come.