Her secretly getting married to a Servicemember who is/was PCSing to Germany makes the most sense to me, but here's another potential military angle:
Looking at the photo she posted of her military brother, it gives a few more details:
He's not in the Army. The combat shirt and Desert MARPAT camo show that he is either a Marine, or a US Navy Corpsman (which are basically medics for Marine units who are formally in the Navy, but are posted in Marine Divisions). The subdued patch on his arm looks like the 4th Marine Division patch to me, but it's hard to tell.
Why is this important? Because while the Army and Air Force have plenty of bases in Germany, the US Marines have little to no opportunity to be posted overseas to Germany (with one possible exception I'll talk about after). If they're stationed in Europe, it will be to Naval Station Rota, in Spain. I don't know if land crossing is more lax, but it could be possible that she was able to tag into Spain to her brother, then cross over land into Germany?
The only exception that a Marine would be posted to Germany is that US Marines are embassy security for all US Embassies around the world, including the one in Germany. Perhaps if her brother worked as embassy security, if there was some way of slipping her into the country in the middle of all this, his connections in the embassy would be the people most likely of being able to achieve that.
Or, it's very well possible that her brother did what a lot of Marines did when they found they couldn't get promoted above E-4 if they stayed in the Marines after the surge, and just ETSed with the Marines and signed up with Army. Who knows. It's fun to speculate on this dogfucker mystery with all of you, anyway.
Oh, also for the case of her getting married to a servicemember: in the military there are extremely strong incentives for an enlisted soldier to get married (to the point where a lot of dumb privates will marry a stripper or a girl they've known for a week, or even soldiers doing the whole "I now pronounce you Chuck and Larry" con). If you're married, you get given more money in your pay, since instead of having to live in the mold infested shitty barracks where you have to share a room (at least in most bases in the army), you get payed BAS adjusted to the regions cost of living to pay for your rent/morgage and food. So, an E-5 and below enlisted servicemember will be willing to marry practically anything to get out of living in the barracks, where they get waken up at 3am for a surprise "Health and wellness" room inspection. So, I'd say the possibility of some dumb private wanting to marry a dogfucker he barely knows to be a strong possiblity.
Sorry for all the military sperging, hope something in there can help pin this dogfucker down.