I know you are either trying to either ease your mind or to get answers out of concern. Probably both things, actually. I feel for you, I know how hard it cane be when your mind gets wrapped up in these things, especially when it's a loved one we worry about.
The good thing is she did get treatment initially. Hopefully it was curative, but you're right that there can always be a small number of cells remaining after treatment, which is why they follow you closely afterwards.
If she was not a candidate for curative treatment back then and they did surgery to buy time and treated as you all went along to manage symptoms as they grew intolerable for her, then the management may have outstayed its utility and it may be time to reevaluate, switch gears... maybe a more successful treatment has come along since, or maybe some previously inoperable tumors are now in places with better access or have shrunk enough to cut out.
Stomach upset isn't unusual, not in survivors, nothing the general public. It's not specific for cancer, it's just one of tons of symptoms and signs that is here today (or everyday) and gone tomorrow (or never). I have had gastritis from eating gas station food. Freakin' 7-11 taquitos and a Slurpee. Nothing good about that sitting in my gut but it was worse when it missed me so much it ran back up for one last goodbye. urrrrrp So please feel reassured that sometimes the easiest, most likely answer is the answer. It really could be GERD or indigestion or a stomach bug. Try to remember that! <3
Oh, and what do you mean wounds, though? Stomachaches or an ulcer or bruising or rash on the skin? Throwing up blood? This isn't going to be something easy to tell you much about without a minimum of pictures, and even then... the MDs on here are damn good but this is a toughie.
Godd luck to you and your aunt, I hope she feels better soon and you are not left so worried.