oh man, thats a tough one.
one thing to know, infants that age dont even know they are separate from mom. so be very sensitive to that. dont make her scream (like you did, go to her right away) so that she learns that when shes upset or scared or whatever, she can rely on you to respond to her. babies left to cry just cry harder, and then they learn that in order to get attention they have to cry harder - so they learn to cry harder FIRST instead of the lesser cry... you know ? the harder cry though also has a reaction in mom of avoidance. it actually starts making you feel like you dont want anything to do with baby, instead of the instinct that you must do something.
you already have the instinct that you must do something for your baby when shes crying. thats good. dont stop listening to that!! infants as a rule dont sleep well, and even if you had 2 great sleepers before, that doesnt mean that this child will be a good sleeper at all. babies wake up for several life preserving reasons: 1. they wake up often to eat because their tummies are only the size of their fist, and they need to eat often. 2. they wake often to the prevention of sleep issues such as suffocation and SIDS. it is being proven that babies who are often wakers dont die of SIDS. its the babies that sleep all the time that cause more concern for scientists and doctors, and WHY they sleep so hard, so it is a good thing.
so, just be sensitive to whatever sleep habits this child has. you will raise a more confident sleeper if you do. and only you truly have the answers that will help your child. you are "born" with each child with new instincts and new knowledge of what your baby needs. dont listen to family, friends, or random people on advice blogs, listen to your heart. even if it goes against everything you know thus far about babies, even if it goes against everyone you know... just trust that you know what is best.
www.askdrsears.com is a great resource, and has alot of info about sleep.