Many buyers do not realise how a neg/neutral can affect a sellers business in $$$. Some of them are overly critical and it is unfair if it is a minor issue, nothing or if the shipping carrier took longer to deliver and you got the blame, especially as you do not have the right to explain your side of it adequately in the lmited amout of feedback reply space given and then the buyer gets the last word, and it is rare that eBay will remove the feedback.

Do you want to carry a neg on your record for the next 12 months? Tell her the truth, perhaps she will understand the impact she has on a sellers abilitiy to earn an income and moderate her feedback. You did the right thing by blocking her.