Do you mean that she's lagging?
There are a bunch of ways to help with that, but the one I'd try first is to get a nose target (to your hand) or a foot target (to an object that you can position yourself beside, ex. a book or an overturned flowerpot saucer -- this will also give you a head start when you're ready to train pivots and position changes, if you decide to do that) and reinforce heavily for being in the right position relative to you.
I wouldn't expect this to be finished in three days. Three months
might be more reasonable.
If she's offering a Down when you ask for a Sit, that's a good problem to have: it means she's eager to offer answers, so you have a certain amount of cooperation to work with, but she's not 100% clear on which one means what. Quick, fun, happy drills and lots of rewards for the correct answer will help. This is a very, very common issue and it just needs time and practice to clear up.
If she's just four months old, you're making SUPER progress. Take it slow, be patient, and enjoy the puppy days.