https://www.reddit.com/r/grammar/comments/1raroa2/was_vs_were/o6lzs84/
We use the 'subjunctive mood' to talk about hypotheticals or things that are counterfactual to reality (impossible situations).
Ex: If she were real, she would have to be 8 feet tall to match the proportions of that doll.
↥ Here we use "were" (the subjunctive form) to talk about a hypothetical
situation, "If she were real..."
"She was real" is stating a fact (nothing hypothetical or counterfactual).
"I have accepted that she was real." (present tense, perfect aspect)
"I had accepted that she was real." (past perfect) often used to indicate
that an action was completed.
This was before "that action had been completed":
This was before "I had accepted that she was real."
"I was skeptical of it."
"I was skeptical of it even before I had accepted that she was real."
There is nothing hypothetical or counterfactual here. You could even say:
"I never accepted that she was real."
If you can replace "accepted she was real" with "accepted the fact that she was real,"
then "was" is the correct choice.