Oh mama, I want to send big hugs your way! I completely believe that your daughter knows her twin is gone and feels sadness. My twins are only 8 weeks old and we have definitely noticed that they are more comfortable together than apart...especially in the evening.
I don't have experience with your situation, but I just wanted to say that it sound like you are doing all that you can do in that difficult situation. My 5yo is having difficulties adjusting to not getting enough attention with the new babies here. I have found that the more present and "in the moment" I am during the time we have together (even if it is very short) the more it helps. Sort of a quality vs quantity. The statement that I use in my mind is
"BE HERE NOW". This helps me to not feel so scattered when spending time with my children.
Your daughters are so lucky to have you as their mama. The I also encourage you to keep coming back to this forum for support! Keep letting us know how you are doing.
Mama to Ainsley (7/01) , Finley (10/06) and Jade (10/06)