I agree to Naoki-san. As you and others say, ちゃって is from ちゃう, and ちゃう is the casual way to say てしまう.
I suppose there are two usage for Vてしまう: 1) to V **in an unexpected way**. ≒ You cannot control to or not to do so by yourself.
2) to V completely ≒ to finish V-ing.
Now you might guess usage #1 will be adequate to 考えちゃって. I’d say 一人で考えちゃって means like “I cannot stop thinking to myself. I do so without intention.”
Additionally, I don’t think ちゃって is a feminine word, but just casual and like conversational. Men can also use it. But try not to speak with long えsound at the end like: ちゃってぇ~, that is feminine, more like childish, or add suffix ね or さ at the end ~しちゃってね/~しちゃってさ; good for both male and female.
e.g. 最近彼女のことばかり考えちゃって。 Well, you might fall in love with her!?