<<With my friend I opened that door but tried to help her to see the truth
I am curious, what is "the truth" that you want your friend to see?
<<and I think she became nervous
She absolutely became nervous if you told her something that contradicted the watchtower society.
<<when I started planting a seed of doubt in her mind.
I doubt that you did that. JWs are indoctrinated to immediately dismiss anything from their mind that comes from the "not we".
<<I would say, "sure we can study together....but let's start from the <<begining of the Bible and the Bible only."
There are very few JWs who could conduct a study like that. JWs by and large do NOT know the Bible. They know the Watchtower books. Personally, I would accept an offer from someone to conduct a Bible study that way when I was a JW, but most JWs couldn't conduct a study that way if they wanted to, which they won't want to because it is not following the "God's Holy Spirit directed organization's" arrangement.