I don't grow Gardenia, but I found this:
https://www.hunker.com/1342627....
I feel like because you have inherited the care of this, you should find out if your mom fertilized a skosh too much. Humidity wreaks havoc for me this time of year, and I seem to have to watch the plants with thin leaves like a hawk.
I hope you will hear from some gardenia growers for a more experienced insight.
Good luck.
