What if......

What if you emailed her the letter - unedited - and at the end said, as someone else suggested: "I am sorry if I am crossing any boundaries with this email, I didn't want to wait for a month for you to have the letter. I would like to discuss email boundaries when we meet. If you could please let me know you got this, a simple 'got it' will work, I'd appreciate it, and will look forward to seeing you in a month."

That way your T doesn't knows you don't expect to engage her in conversation via email, and you are acknowledging any potential boundary violation, and setting up for a boundary discussion upon your return.