I am on felony probation in a small county in Texas and I got pulled over by a bicycle cop in a big town across the way and was issued a open container ticket for a beer bottle my passenger had in the car. Long story short... should I tell my PO about the ticket or will this traffic-ticket fly under the radar and maybe she won't know ? Kind of scared and need advise...

Do you really want to take the "maybe" chance, and yes it may fly under, or maybe the officer who did it notices you are on probation and sends him a email. And you said it, small county, in the small one I grew up in, they would know in a few weeks anyway.

I would tell them, since the violation is a lot less than the violation for not notification

I told my PO like you said and she said that she is happy I told her and that she is mostly concerned that I take care of the ticket,. you were right!!