I know that after or before someone's ears pops because of pressure changes, he/she can hear the sound such as laughter. But can these two things ("her ears popped with pressure" and "she can hear the laughter") happen at the same time?
Yes, of course they can. What happens when your ears feel 'full' like on an aeroplane is that the air pressure in the middle ear is different from the air pressure outside. When you 'pop' your ears, you push open the Eustachian tubes that connect the middle ear to the throat and make the pressure equal. No matter what the air pressure, the air still conducts sounds. The difference is that your ear drum moves a bit less if the middle ear pressure and outside pressure is different, thus why sound is muffled before you pop your ears.