Okay so I'm a little off my game today! :-) Sorry, when I first responded to your post, I didn't see your signature line showing that you divorced just last October and that your kids are 7 and 3.
So seeing that, while it doesn't change my opinion that you need to get out and do your GAL activities, I do understand how this divorce is very recent and the pain from all of that is very fresh.
Also, with the age of your kids being only 3 and 7, I'm not sure exactly why your ex-Wife feels a need to tell them she is dating. The 3 year old certainly won't have any idea what that means. However, that being said there still unfortunately isn't anything you can do to stop her even if your advice that there is no need to rush into telling them is the wise choice. Best you can hope for is that after she left the meeting your opinion and advice on this absorbed into her mind and she takes it into consideration.