Not getting text notifications since buying an apple watch

I just got an apple watch a couple of months ago and now I constantly miss text messages because they do not make any sound on the phone or the watch. Now, I hate to admit, I'm somewhat familiar w/ this as my mother, who's had the watch & phone for a couple of years, has sworn to me multiple times that she doesn't get the notification when I text her & I have accused her of lying and ignoring me. I've had an Iphone for years and never had any problems so just assumed this was user error on her part or worse, intentional - until I got my own watch. Why is this happening and how can it be fixed? I have to constantly check my watch or phone now to make sure I don't miss important text messages. It was so much easier when I just had an iphone and a fitbit - where-by I was notified of texts on both the fitbit and my phone.