I started a new position in October which rescued me from a very toxic situation. I was thrilled to start a new journey in a less stressful environment. The position I took was created solely for me, a combination of a personal assistant and charitable organization manager. Because of this, I work in my boss's corporate office. When I started, the bills were paid by another colleague. They have since slowly been transitioned to me. The issue I am having is the coworker who handled the bills earlier now undermines me via email with our boss copied every opportunity she gets. It has turned into an email battle that I remove our boss from because he doesn't need to see the back and forth. I am trying to make things easier for everyone involved while attempting to exclude people who do not need to be part of the transaction. An example is, the coworker and I were sent an email requesting a charitable donation be made. Per the email, the donation could be made by phone, email, online, etc. I replied immediately that I would handle by phone. Within moments, after my boss replied with thank you, the coworker suggested we place the donation by wire, which now would involve three other people. My boss stated for us to handle it as we saw fit - read, I don't care, just deal with it. That's when I removed him from the email and the back and forth started. The end result was that I asked her to at least give me a few minutes to research the best way to handle the situation before jumping the gun and automatically delegating the task to other people. This is not the first time this has happened.
I do not want to be disrespectful in any capacity, however I also feel as though I am being admonished and condescended to constantly. I could understand if I had never had a job before, however I have managed the lives of numerous people and handled their bills; this is not my first rodeo. It was suggested to me that this coworker, along with another, may feel as though they are being pushed out by the company and I am being groomed to replace them (they are both nearing retirement age). Both have been there 20+ years, however this is not the type of business that would force people out.
I have no problem standing up for myself and stating that I should not be treated a certain way. Working from home and communicating by email though, now has me at a loss. I have told this person over the phone it is not okay to talk to me or treat me a certain way, and she has acknowledged it. Undermining me and copying my boss is a new and unfair tactic. Any thoughts on how I should approach it without coming across as combative, or am I being too sensitive and should just let it go?