This is an update to my PostSecret dilemma.
To elaborate on the status of our friendship: I do know her very well, so I took a chance and sent her an email.
Thankfully, in this case, she had no idea what PostSecret even was, but she did guess which card I thought was hers and said the writing on it was eerily similar.
She actually thanked me for being concerned and reaching out to her, even though it was a difficult subject. So, in the end it all worked out.
Thank you for all your advice! I really did take note of all of it, but in the end realised that to be a great friend sometimes you need to ask uncomfortable questions and be prepared for whatever the answer might be.