How should I discipline my pup?

My pup is a 6 month pit mix (I think with doberman) and her name is princess. I got her from the shelter about a month ago and she pretty much became potty trained within the first week and adopted the habit of holding it, and telling us when she needs to go very quickly. Before two days ago the only accident she had was of not holding it, but she definitely told me that she needed to go so I knew it was my fault and I didn't do anything but clean it. But the other night she pooped in the room and it shocked me because she never just poops in the house. I was upset so I did sternly told her no, not quite a yell but it was on the louder side. And also the poop was very soft, but I thought it was because of the food change. But then a couple minutes or maybe an hour later she pooped again and it was softer and at this point I was upset but starting to be a bit worried, and then she pooped again, the poop was extremely soft almost liquidy at this point and by this point I was definitely worried. So any help with that situation would be great because I think something could be wrong. Now that you have backstory, we fasted her for 24 hours and gave her less food afterwards because I saw online that's what you should do for diarrhea. This morning after the fast she had a solid poop and I celebrated because I thought everything was over, I was wrong...it was not
Within the last two hours she's pooped 3 times, one time being in her crate (which she ate sadly) which I put her after her first poop which brings us to the discipline part (Sorry for the long beginning I wanted to make sure and include anything that could affect her behavior) because the first poop wasn't as soft as the next two, and I thought she was better because of the earlier hard poo, I got very upset because she always tells us when she needs to go but in this case she simply got off her bed and squatted. And I feel so bad because I did hit her twice, not very hard I've done it twice before but it was always the lightest tap that didn't even phased her. This time I think it did hurt and after she pooped twice more I felt even worse because I realized it was still more diarrhea. I don't want a hand shy dog and after the hit she flinched when I was moving my hand, which is what brought me here. The two questions I have are 1 how should I discipline her the best because I see many mixed opinions and I would like a more fact based answer. Two is everywhere I look I always see that a stern "no" it's a good way to discipline them to know the behavior is wrong but hitting and yelling are unhelpful and usually have a negative affect because the dog doesn't know why you're hitting them or yelling. But this statement seems to contradict itself because if they don't know why you're hitting and yelling how would they know why you're sternly talking to them saying no and stop the behavior because of it. I just wants what's best for her but I honestly don't know what way is really the right way. Anything is welcome I just want to do right by my princess, and ill be completely accepting if I am wrong.