K.,
I'm sorry for you both, this is going to be hard.
Your daughter is going to be upset and miss her Daddy. There's very little you cando to prevent that, she loves him. My best advice wouldbe to work hard during his absence to help her feel connected to him even though he's not right there.
Put together a string of construction paper cutouts, hearts or flags or something, one for each day he's gone. Every night, let her rip one item off, for one less day till he comes home. as the string gets shorter, she'll get excited about him coming home.
Talk about him all the time. Have a picture in her room where she can talk to Daddy. Before bed, both of you sit down and tell him all about your day, and what you're going to do tomorrow. Help her tell him she loves him and misses him, and can't wait till he gets home.
Let her color pictures for him and put them in letters to him. She will love to do this while you are writing to him, and let him know when you get letters from him. Tell her how much he misses her, and how he loves her pictures and can't wait to come home to her.
At Christmas, and if her birthday falls during his absence, have a special present for her that Daddy left. Make sure he plays a part in all of the special things that go on in his absence.
For yourself, look for a support network of other Reserves wives. They can help you through this time, both for yourself, and for your daughter. Those ladies are rocks, and they've all been where you are. Military wives are some of the strongest women in the world, and every last one has my respect and admiration.
Good luck , K.!