I certainly think that Plath deserves credit for challenging conventions.  She was not afraid to challenge poetic conventions of the day in the idea of ensuring that her work was an accurate reflection of what she wanted in it.  At the same time, Plath displayed an almost unabashed passion towards ensuring that her work could bring out the emotional disintegration that was happening in her mind and how she felt about her world.  For Plath, she challenged the convention of the artist being separated from their work and embraced the idea that the artists is their work and their identity is within the work created.  This is seen in Plath's poem "Daddy."  From a conventions point of view, Plath challenges the idea that subterranean messages cannot be conveyed through the work via sound.  Plath speaks from a position whereby her pain and her hurt is something that almost transcends language.  Yet, Plath realizes that, as a poet, language is all she possesses in order to make sense of her pain and suffering at the hands of her father.  The sound of "ooo" is something in the lines of the poem, following the cadence and rhyme, almost using the poetic conventions to bring out a sound of her suffering as an articulation of it.  I think that this is an example of how Plath challenges convention, pushing the bounds of poetry in terms of what it can be and what it can mean to the poet.  Plath has to be seen as daring in this.  She does not capitulate as to accepting what poetry is and leaving it at that.  Rather, she seeks to construct a domain of what it can be and within this, there is a level of dare that has to receive credit.