Painkillers bad on stomach?

Excuse me if this isn't the right subreddit to post this in or if the question has been asked a hundred times already (i searched a bit but didn't find), but its 3 am here and I'm going crazy and can't bother to search longer... My mom is in quite a bit of pain in the area of the liver/upper stomach or whatever, and refuses to take a painkiller since she always says that they hurt her stomach and are actually bad for it and since it might be stomach related, it would make it just worse... (she does take them rarely though, not generally opposed to them) i always wondered if she is just messed up or if there is a lot of truth in that... could anyone point me to an answer if possible or at least hint to where the answer might already be?

Again, apologies if this doesnt fit, but I'm just trying to help her cause i feel like a painkiller would help...