In these situations, your partner really should be mature enough to think about the shoe being on the other foot. How would she feel if you got a text from a girl every day calling you sexy?
It's not really about you not trusting her... Because I am certain you do...
But even though in all likelyhood it is completely innocent, in a good relationship with understanding and mutual respect, each partner should be aware of the other ones feelings and if anything go out of their way to ensure they are encouraging nothing that could breed an insecurity.
This is where women are frequently hypocritical. Though thankfully not all of them. My current girlfriend would not tolerate anyone other than me calling her sexy. If a guy friend did it once she would tell him that its not appropriate. If he did it twice, he would be removed from facebook/phone number deleted and ignored.
I wouldn't ever ask her to do the above, she just would. This is good as it breeds trust and has encouraged me to act the same with the women that come on to me, or any female friends I have who cross that line.