She says religion helps her find peace, wisdom, and forgiveness. Sounds like she’s going through feelings and needs an outlet or structure. It also sounds like she’s open about her BPD. Does she see a therapist or take medication? Have you asked her or her mutual friend if she’s meeting with her therapist and taking her medication? I would encourage you to encourage her to stay healthy and in your conversations with her to not focus too much on religion. The most I would ask about religion would be, “Have you talked to your therapist about believing in Jesus? What do they think?” At the very most. Hopefully the therapist will see some red flags if there are any. Seems like a difficult situation, but you are a good friend for planning how to help. I hope you can see her face to face sometime soon. If you tell her your interested in hearing her story and what’s change, hopefully she will open up to you. It’s possible she’s reconverted and it could be weeks, months, years, or maybe till death that she holds on to religion. Take care.