Yes, generally that’s what happens, it dilates arterial blood vessels. Often causes headaches and a flushing sensation until people get used to it. We use it in cardiac care (though not nearly as often as previously, more so in pill form now) and give tylenol with it or put it farther away from the head, like on a leg (which your friend can’t do since it’s directed to be on her breast tissue). It would be unusual to dilate a pupil (personally have never seen that happen with many years of use), but strange and rare things can sometimes happen with some of these meds (which I have had happen myself with a different type of med).
How is her pupil now? Hopefully back to normal. I’m sure they told her to stop using the cream, right? No doubt the surgeon just wanted to rule out anything serious to the eye or a neurological event after the surgery, etc. And it’s prudent for her to be checked out by an opthalmologist. But hopefully it was just an unwanted side effect of the cream that won’t happen again if it’s not used again. She’ll have to talk to the surgeon about how that will affect the breast tissue. I imagine it’s used just to help blood flow through that area. (Have not had that experience myself.) Sorry that happened to her with everything else going on, I’m sure it was scary.