I have already written about her achievements.
since the question is an "assess" question, I was wondering if these 2 points are strong enough:
her deteriorating relationship with nero= she cannot influence and rule through him= hence her potential for achievements is lost
her premature death due to Nero's loathe for her= premature and complete lost of achievements and potential for achievements
Hey!! How cool is Agrippina hey, just wanted to get that out there. Enjoyed learning about her so much last year.
I think you first point is strong, and you could extend that to the fact that she greatly relied on her relationship with ALL the significant men in her life to secure the position in which she could enact the most influence (eg. Claudius, Seneca, etc.). You can look at though to what extent this was a situation whereby she was just kinda in the right place at the right time, or whether she actively secured these conditions in order to maintain power (ie. it was an active and calculated decision). I think your second point is a little bit weaker though, and is more so just an extension of your first point. However i do think that important point that can be made is the fact that after her death Nero had many statues and art dedicated to her destroyed, which manipulates the evidence of her significance to history!