Is this weird behavior for a step mother?

My 13-year old son lives with his father and stepmother, and I get him on the weekends. For a while now, I have thought that his stepmother has been very controlling of my son and what goes on in his life, from discipline, to any decisions regarding him, even trying to overstep her bounds with me as his mother (i.e., trying to overrule my actions his mother). I've noticed the following peculiar behaviors and don't think that they are appropriate, and just want to get others' opinions on whether I am jumping to conclusions are should I do something about them? She has a Myspace page, where 90% of the pictures and blogs that she makes are about my son. She regularly messages my son's friends back and forth (as evidenced by the comments on her page and theirs). When my son is with me on the weekends, she text messages him on his cell phone constantly. In a 3-month period of time, over the course of only 7 weekends, I counted a total of 79 text messages ... one time, she texted him for 2 hours straight, and another for an hour straight. She sends him messages when he is with me that she misses and loves him ... one of which said something to the effect that "she had no one to roll over her to wake her up, and that made her sad." These are just a few things, but in comparison to contacts by his father when my son is with me, she dominates ... my ex only contacts him when he is with me on occasion ... no where near the amount of time that she does. I just think the fact that she is always contacting my son when he is with me, and the context of her messages, and the fact that she has conversations with my son's friends is indicative of some type of obsession. I would appreciate anyone's comments or sharing similar situations.