How to cite an author who does not capltalize her name if you are beginning a sentence with her name
In general, I would say that one should do what they do:
With "of" or "from" names, one normally capitalises ("De Gaulle", "Von Neumann") so that's generally a safe choice, though some may drop it when their surname is used alone, so if you know that the person in question does so (perhaps from seeing a reference to their own work doing so), then drop it too.
With another lower-case name like k.d. lang or bell hooks, stay lower-case. Because why not? It's their name, so unless you learn that they themselves capitalise it at the start of sentences, or unless you're inclined to just capitalise it all the time (which would strike me as rude, but at least consistently so), why not just follow them.
E. E. Cummings is a special case. There's a myth that E. E. Cummings liked to spell his name as e. e. cummings. But he didn't, and the myth seems to have arisen from a mixture of one typographical decision on a book cover made by an editor, and his using lowercase where one would normally capitliase in many of his poems. Therefore always capitalise E. E. Cummings, whether at the start of a sentence or not.
And if a style-guide you have to follow insists that you must capitliase, then of course you therefore must, though I'd try rephrasing to avoid it, first.
It depends on what style guide you're using.
Chicago Manual of Style suggests respecting the lowercase form and rewriting the sentence to avoid beginning the sentence with it.
APA says to use the lowercase form in reference citations, but to capitalize when starting sentences or following colons.
Other style guides will have their own conventions.