iPhone 7 suddenly shut down, battery replacement doesn't work

Hey everyone!

My sister came to me after her iPhone 7 had died. She was driving home in her car listening to music and everything was working fine. Once she got home, she put her phone in her pocket. Less than 5 minutes later, she took her phone out of her pocket and it wouldn’t turn on. I tried doing a soft reset with no luck. Tried plugging in the phone then soft resetting it, did not work. I even plugged it into my computer and tried soft resetting it and putting it into DFU mode with no luck.

At that point I ordered a battery and charging port. Once they got here, I put the new battery in with no luck. No power, no nothing. When I put my finger on the logic board after holding down the power button it gets warm, but I am still getting no signs of life. It couldn’t be the LCD either because it hadn’t been dropped prior as well as there’s no vibration when flipping the ringer.

Not sure what is happening or if anyone has any ideas.

Thank you!