One user has reported that no one appears to receive any notifications when she posts - I've tested this alongside my account (admin) and noticed the contrast in how our copies of teams behaves. When I message her privately she will receive a banner pop up (windows notification at bottom right) as well as her chat icon will be highlighted with a red 1 to show she has received a direct message. When the situations are flipped I receive (and other users) no such notification - in fact initially the user did not appear in my private chat list at all (after they first sent a message) and I only saw their message when I attempted to open a new chat to message them directly.
After some further testing I was eventually receiving banner notifications but still no notifications within the app itself.
1.) What happens when she does this from the web app as opposed to the desktop app (https://teams.microsoft.com) - any change? 2.) Do you get the correct notifications with all other users who do the same? So not you specifically, but someone else or a few others in the office/organisation
Sounds like there is an issue with the user. I would be tempted to raise a ticket to support on this particular one.