Don't shriek back. You should have only one yeller per household, so keep your voice soft and stay calm. Eventually your baby will adopt your tone, and in the meantime it will be far more soothing than adding another screech to the mix.
Accept help. Don't feel guilty! Your job is to be the best mom that you can be, and sometimes that can mean letting others help you. To avoid losing your temper, let Dad take her outside for some air.
Look for patterns. Does she scream at certain times, like when she's hungry, bored, or tired? Most shriekers at this age yell as a way to express frustration. You can help by giving her the words she's trying to say. If she screeches while squirming in her stroller, ask her, "Out?" and demonstrate what you mean. As she picks up on these cues and learns to communicate what she needs, she'll have less reason to scream.
Ignore critical stares. Apologize if you have to, but beyond that, there's not much you can do. Most of us have been there, and you can take solace in knowing that this stage won't last forever.