First off: fantastic game.  Looks and sounds great, runs smoothly.  No real complaints on my part about anything.  That said...

Mechanically, it does get too easy to keep her happiness maxed out once her production and size get to a certain point.  The simplest solution might be to have a "golden range" of fullness for milking: draining her past halfway empty might have drastically reduced, or even no effect.  Reducing milking effectiveness and bumping up happiness bonuses from great/perfect drinks should help keep the aim on, well, making good drinks as quickly as possible.

This might just be me, but I tend to have trouble telling the difference between chocolate sauce and coffee when the amount requested is small.  It'd be great if the stripe pattern were more obvious, especially at the bottom of the "layer".

There are a few typoes--when you beat Chaos Mode, it says: "What...?  Well uh... Congrats on beating whatever this way.  Wow."  I believe you meant for "way" to be "was".  Additionally, there are a couple of Barbra's dialogue lines that appear to have errors.  In, "They have grown allready so big!" the word "allready" should be "already", and would be more natural if the phrase was, "They have already grown so big!"  There's also a joke about a milkman but he's only referred to as "milk".

As for suggestions on additions...  More complete statistics info at the end screen would be nice.  It'd be neat to see the rates on drink quality.  Additionally, being able to add customer portrats is super neat, and I wonder how possible it is to expose Barbra's dialogue to modding, allowing players to modify and add their own lines (via XML or JSON, perhaps).  Having attributes and content separated from programming code (if it's not already) will help make future work easier to do anyway.  Maybe that's a bit of a stretch to ask for, though...  I just really like a lot of the things Barbra says and want to give her even more to talk about.

At any rate, thanks for all the work you've put in!  I know it's probably going to be a good while, but I look forward to when you can get more work done on this game.