Crying 3 yr old

Need some advice,

I have a three year old who has been crying constantly. She has been doing this for the last two weeks on and off. I've had her since she was a baby and she's always been very needy. She is very manipulative and if things don't go her way she cries. She went on a vacation just her and her parents for a week, so had all the attention in the world. Since she has been back, she has been crying. I've done the rewards sheet and it doesn't help. She cries out of the blue, so it's not that we are doing an activity she doesn't like and starts to cry. There is no rhyme or reason. ( Mom is at home with baby sister, so she wants to stay at home too) She wants the attention. I've tried ignoring the behaviour, but it doesn't change. If I tell her to go to bed and get up once she is in a better mood. She will stay in bed all day. She doesn't want to participate in activities. Any ideas?

Maybe she is feeling unhappy because she knows Mom is home with sister and she isn't.

I had a 4 year old who did this for her final 3 months here. I had her since she was 14 months. This girl was just unhappy too. The parents were curious why but didn't seem concerned. I tried everything to help her and so did my husband who would sit with her and give her special attention and try to talk about what was bothering her. She left for school in this condition.

Sometimes I think these kids might be depression prone. I would just try to be supportive and give her positive feedback when she is not crying. My dcg was always quite happy to lay in bed too if I had let her. I get your frustration though as it has a bad effect on the mood in the daycare.

If a child is crying and my attempts to redirect and refocus aren't working than I will tell the child that it is okay to cry but it's disrupting our friends so they will need to sit in the library with a book and cry or sit in their bed and cry. This usually stops the crying but if it doesn't, they will go and have their cry and when they are ready they come back.