HUgs Becky. I am so sorry to hear your little one is waking again. It sounds like it could be teething again, but here is a thought. You said she's been doing it about a month and she's 13 months old. Did you switch her to cows milk at 12 months? Maybe it's not agreeing with her? Just a random thought. If it continues I would check with your baby's Dr. I do know from experience (I'm the mom of 3 LOL) that all my kids woke up in the night during teething. I especially remember my oldest doing it.
Hugs to you and here's to hoping you both get more sleep soon!
Shannon