A huge presumption that she was not saved and that whose heart was opened is her being regenerated.
She could in fact have already been saved, since she was one who worshiped God.
And maybe her heart was opened as a believer and and she learned more from Paul and was baptized.
Again, based on presupposition to make it fit a faulty doctrine.
I will answer this charge for the benefit of others because I know it will make no difference to you. Perhaps this translation will help some to see:
Act_16:14
And a certain woman by name, Lydia, a dealer in purple dyes, of [the] city of Thyatira, worshiping God, heard: of whom the Lord had opened up the heart, to take heed to things being spoken of by Paul. (Translation by Dr. Alfred Marshall, from the Nestle Interlinear Greek -English New Testament, 1974 edition.)
Let's now look at the important point I was making, in this verse.
v 14b, was presently worshiping (present active participle verb
) God, had heard (imperfect active indicative verb, the imperfect tense, puts emphasis on a past event, with continuing results.
: of whom the Lord had opened (aorist active indicative verb, sometime in the past.
) up the heart, to take heed to things being spoken of by Paul.
So you can clearly see, that Lydia's heart had been opened in the past by the Lord along with her hearing and she was now able to be worshiping in the present, while Paul was speaking.
It's not difficult to understand, as long as one has Grace and puts sometime into study. It is a dangerous thing for one to give interpretations when they only have a little knowledge. Also, one can interpret the Scriptures with the aid of the Holy Spirit and come to the Truth but it sure helps if you are fluent in the old Koine Greek Language, that is Biblical Greek not modern Greek. It helps clear up a lot of difficult passages. Not boasting, it is just a fact.