If your teacher has assigned an essay which requires you to analyze theme, then your thesis works well (it is a little wordy, though, so try to combine some phrases).

However, if your essay is supposed to analyze Dickinson's poetic techniques, diction, or an area more specific than theme, then you need to address that in your thesis. 

Hmmm.  It's a bit vague.  It's listing themes that might apply to any three of her poems.  You could replace the titles with "I Never Saw a Moor," "Because I Could Not Stop for Death," and "A Bird Came Down a Walk," and still not know the differences or similarities between the poems.

You need to be more specific.  For three poems, find a common thread that is not a listing of broad themes only.  Does the speaker use similar imagery that suggests loneliness?  Is nature lonely for the speaker?

Dickinson often uses nature not as a source of comfort, like a Romantic, but as something insensate and alienating.  Her speakers seem lost outside.  Dig deeper here, maybe.