Would sending her a text be a mistake?

Recently, I discovered why my first girlfriend broke up with me, and it was because her best friend sabotaged the relationship.
It had been 3 years since we broke up, and I just wanted to put it to rest in my mind. So I sent her a Facebook message, just setting the record straight.
Although she never responded, I recently ran into her best friend and she gave me a lot of grief, but never said specifically what she was talking about.

It's been roughly six months since I sent the message, and I never got a confirmation it was read.

The other day, I found the wallet I used to use, and I found the card she gave me with her cell phone number on it. Is texting her a mute point now? Or would it be worth a try?
Would sending her a text be a mistake?
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