Poor girl
I feel for her. My (former) BF (then of 6 years) was deployed for 18 months in Kuwait/Iraq. While he was away, I worked in the "family support unit" and tried to help a lot of wives, sisters, moms, Aunts, uncles, etc. with their issues at home. It's very hard but it is very do-able. This is my advice...some might not agree...
At 19, she is still so young and vibrant. She's got a lot to do and plenty to keep her busy. If it were my relative, I would encourage her to go out with friends, be social, join new clubs and activities and live life without guilt that he is over there fighting in a war and she continues life at home without him. That can be hard to do. So many times I would be having fun, finally with my mind off of him and where he was, and then all of a sudden, it would hit me and that was the end of my fun. He's got his job to do and she has hers.
Make sure she has a phone that he can call without interruption or missing her. MY BF and I spoke about once per week. I had a cell phone that he called, mostly in the middle of the night here (EST time), b/c that was late afternoon time there. I tried not to expect the call but there was one time when he called and I wasn't there and I wanted to die. From there on, I forwarded all calls to my cell if I was not at home.
Don't let her watch the news. If a plane gets hit or a soldier dies, she will be in turmoil until he calls b/c she won't know if he is safe. Since that can sometimes be days or weeks, she can't put herself through that. I also avoided miliatry based movies. It sounds stupid but that junk just puts ideas in your head. To this day, there are still movies I can't watch.
Part of the difficulty is that all of a sudden, you are thinking for two people, making decisions for two people, doing everything for two people. YOu may not know how to do some of it b/c he always did, etc. Remind her that she is doing well with everything every so often. Help her with things that she might not know how to handle (ie: fixing the sink). Grab her and make her go out to take her mind off things when she gets that glazed over look.
When he gets home, a whole new challenge begins. This is where my BF and I didn't succeed (we recently broke up after a 9 year relationship). It's hard to start over again after a long absence and after what each of them have been through. After all, they will each have challenges and emotional issues stemming from the deployment. My advice? After he's been home for a bit, take a weekend away and have some fun. If things aren't looking right in the relationship after a reasonable time, get help immediately.
It's hard. But like I said, it is do-able. she's already very lucky to have family thinking of her and finding ways to make life easier.
I hope that he stays safe and she stays happy in his absence. My thoughts are with them both