There seems to be three issues being discussed –
1. Whether or not it is ok to rely on ingredients alone to determine the kashrus status of a product.
2. Whether or not it is ok that the OP opened her mouth to a complete stranger about something that did not affect her.
3. Whether or not it is Lashon Hara to discuss this at all.
My opinions are as follows:
1. It is imperative that every Jew follows a Rabbi for everything. If your Rabbi says this practice is ok, then it is. If he does not, then it is now. You can argue until your face turns blue, but those of us who follow the ruling that it is ok trust our rav, so it really doesn’t matter how you dispute it.
2. Personally, as I stated earlier, I feel that it was absolutely none of her business.
3. I’ll have to abstain from commenting, as I am not well versed enough on the laws of shmiras halashon. But as a side point, there is so much lashon hara that goes on here, that if anyone here is really so concerned, s/he would stay away from these forums altogether (which is exactly why I usually do… but nobody’s perfect).