Was it rude for a preacher to preach the gospel?
Was it rude for the lady to approach the OP at the funeral of his grandmother? yes, I do agree with that.
The latter of the two. I wouldn't expect to be verbally attacked for my religious beliefs while paying respect to the deceased at a funeral.
I was appauled at how 'Christian' she acted towards me. 
Man, an insensitive funeral service sure does burn, doesn't it?
I regret that happened to you too.