Honestly, there are always deals. But I'm sure they will hinge off of the iPhone 12 release. BOGO on the non pro models possibly. They will definitely take that X off your hands, but you might not love the price. If she is in good/great shape take a look at the re-sale value. Swappa, eBay ect.
At least for me switching carriers has been annoying. I did an experiment recently and tried all carriers, TMO, ATT, & VZW. I ended back at TMO. I switch phones like underwear and TMO ends up being the easiest and most friendly. Example. ATT most of the time you need an ATT branded phone in order for WiFi calling to work (non iphone). Same with VZW. I also did eSim on all of them which inherently goes against someone like me who switches phones all the time. VZW had their heads up their a$$. It took several calls and wasted time to get it to work. I know this wasn't exactly your question lol, but I like to ramble on this topic. I have a lot more too 🤯. I'm not trying to persuade you at all, but I also wanted to mention TMO customer service is leagues above the others in effectiveness and timeliness.