are we doing something wrong?

so while commenting on another's blog, I found myself thinking about how much Goose talks (or doesn't, as the case may be) and find myself wondering if we're doing something wrong? G will be 15 months old tomorrow (okay, technically today, as it's now after midnight - why am I not sleeping?? good question. I do have to work in the morning... ack. off topic.) back to the topic at hand --> and really the only words she says consistently or very often are "mom, momma, hi, uh oh, ball" and sometimes she says "da dee"... she doesn't sign (which is completely our fault... I had intended to start with her a while back... but only knew a few signs, kept forgetting to pick up a Baby Sign book, and here we are, still haven't done it, FAIL.) everything else she says - pure gibberish... I'm sure she knows what she is saying, but me? not a clue. are we talking too much and not letting her practice words on us? are we not talking enough and teaching her words she can use? her 15 month checkup is April 20th - and I'm a little anxious that the Dr. is going to say "what is she saying" and when I tell her G's list, she'll say "uhh... that's it?" and I'm also having some guilt that we haven't even tried to start teaching her body parts... like "nose, eyes, ears" etc... the only one I say often is "feet" and usually it follows "who has stinky...?" after removing her socks while changing her diaper/clothes... (by the way, she thinks this is hilarious when I smell her feet and either loudly exclaim "ohhh!" or "peeeeyyooooooooo - stinky feet!" and gives me great big belly laughs - which I love) :) so yeah... anyway. my 15 month old has like 5 understandable words in her vocabulary... so, are we doing something wrong? what can we do better? how do we expand her vocab? read more? talk more? talk less? I'm open to suggestions, advice, etc (but please be nice... I'm very good at the guilt-trip on my own, thanks!)