I am a former Navy wife. We had 2 children going into the Navy & 2 more when we got out. My husband served on submarines, so he would be gone 3 months, home 3 months, and so on.
One thing that helped a great deal with our children was to video tape Dad reading books to them. They would get the book out that he was reading & follow along with him. He also recorded his voice on cassette tape and we could play it in the car while driving. If you know he's going to be gone say 30 days, you could buy 3 small gifts 'from daddy' and have her open 1 every 10 days. She's not to know there are other gifts or she'll want them NOW, LOL.
Some of our friends husbands served on the Nimitz. They knew how many days their husbands would be gone so they'd cut paper chain links for X amount of days. They would either, link them all together & remove one each day OR add one to each day & when he got home this chain would be decoration for him homecoming. On a submarine we couldn't do that, their missions were secretive (silent service and all) so we opted to add a chain and hide the links. That way if anyone came over, they wouldn't know if he was coming home in X amount of links or what. Also we didn't tell the children exactly when daddy was coming home since loose lips delay ships. So when I would pull that LAST link, we'd have a mini-celebration for it. That silent service thing was serious too. If we talked openly about their return date & word got back to command, they changed the return date & we didn't get the new date!
Anyway, I digress. Little gifts, pictures of him, reading stories on tape/video, making a paper chain link all helped with us. Another thing, if she likes to color, he could sit & color 'with her' on video as well. Then have him leave the picture he colored & when "he's done" you give it to her!
Being together with other military children will help too and the Mom's groups are helpful for you as well.
Best of luck to you & thank you to you & your husband for making this sacrifice for us!