A few differences (from start to end of the meal) you can expect between the USA and Germany when eating out...
Getting seated: In the USA you will be told where to sit, in Germany you may sit where you like. This also means that in some restaurants, if it is very crowded, strangers will sit at the same table in Germany. This would never happen in the USA.
Water: In the USA you always get water free with the meal. This does not happen in Germany. Easiest way to get free tap water in Germany? Say you need to take some medicine :)
Drinks: It is much more common to drink beer with your meal in Germany (lunch and dinner) than in the USA. Soda is very common in the USA and always comes with free refills (along with other drinks such as coffee and iced tea). Drinks in Germany come with no ice or only one small cube. America loves ice and often it takes up half of the glass (which is okay when you get as many refills as you would like).
Prices: In Germany the price on the menu includes tax. Tax is not included on America menu prices.
Changes: America loves flexibility and decisions. Eggs come in about 10 different versions and salad dressing have about 30 :) You can also almost always make changes to your order (no onions, potatoes instead of fries, etc.). This is possible in Germany but not as common or encouraged. She has also never seen a choice in salad dressing or even bread with a meal.
Service: In Germany the waiter or waitress basically leaves you alone once you have your meal. It is considered reasonable if you need to get the attention of the waiter. Waiters in the USA are overly attentive, often coming over every few minutes asking if everything is okay. If you need to call your waiter over in the USA then it is assumed that he is not being attentive enough.
Paying: In Germany you must ask to pay. The waiter then has you pay right there and often adds up what your ordered in his head without even giving a receipt. In the USA, the waiter often leaves the bill on the table before you are even finished eating. You then put out your card or money out and the waiter picks it up, goes to make change and comes back. You always get a receipt, even when you do not need one, in the USA.
Tips: Tips in Germany are rather small, often if you are only paying for yourself you just round up to the nearest Euro. If you are paying for multiple people you tip a few euros. This is because waiters in Germany make a good amount of money and tips are just extra, not their wage. In the USA tipping is much larger (15-20% of the bill). Waiters in the USA are paid only a few dollars an hour and truly make their money off of tips, making tipping extremely important.
Leftovers: While in the USA you are asked if you would like to take your leftovers home (sometimes even when it is only a few fries), this is much less common in Germany. However, in some restaurants (especially when eating pizza) it is becoming more common to take leftovers home and you do not get as strange of looks as even a few years ago.