You ARE going to see her do things! You are going to see your daughter blossom and grow and learn how to deal with kids her own age. And she'll bring home all sorts of great stories and arts and crafts and you'll be able to see her joy in her own abilities and accomplishments. Truly, this is wonderful. It's NOT the end of your time with her; it's the beginning of a different kind of time with her!
Further, you're giving your baby the gift of one-on-one time with you. Many 2nd or 3rd babies don't get that and I think it's wonderful that you see it that way.
My boys are now teens and we still spend lots of time together, just different from when they were babies. An obvious example...I used to read constantly to my kids and it was sad when they wanted to read on their own. But, now, we all read together. We call them reading fests and we usually kick back in our family room or on someone's bed and we read away. Then, we chat and discuss what we've read. See? Still reading together, just different.
Change is hard, dear mama, but remember the ultimate goal of parenting: raising happy, confident children who can function well on their own. You've taken a positive step towards that goal. That doesn't make the sorrow any less, but it does give it perspective (I hope). My oldest is staring his senior year in high school and not a day goes by that I don't tear up at the thought of driving him to his new college dorm (where ever it may be) and then having to turn around and go home without him. But, through my tears, I think about all the fun--FUN, FUN, FUN--I'm going to have with my youngest because it will be "just us" (well, my husband, too, of course). It doesn't make the sorrow less, just different.
Parenting...it's all "just a phase!" We can't stop the phases, so we might as well embrace the joy in the them.
Hugs, dear mama, and good luck.