She's at the age where she recognizes what she likes and doesn't like, and is beginning natural experiments in cause and effect. She's engaging more with the world around her, and becoming more curious and interested. And she is probably working on some major motor skills now, sitting, scooting or crawling, pulling herself up, experimenting with making deliberate sounds. All of this is extremely stimulating to most babies, and they have a much harder time sleeping.
She is also at a common age for separation anxiety. You leave, and she's not certain you still exist. As odd as it seems, she won't know for awhile yet that you'll be there for her every day, even though you always have been. But now that she's beginning to get it that you are separate from her, and she may feel actual fear when you leave her alone. Putting babies in a separate room in the dark is actually a fairly recent development in human history.
So, she's noticing that she doesn't like being left alone in her room. She may be having trouble falling asleep. She does like Mommy's attention. She notices that screaming gets you to pick her up. Can you introduce a new bedtime tradition, like sitting by her crib and singing or telling her soothing stories in the dark? Patting her back or rubbing her head? I'm guessing she needs something different than what is happening.
Every child is unique when it comes to sleep patterns, and what works for one may have no connection at all to what works for another. But connection with parents is an absolute and legitimate need for babies.