Ok so I'm a fairly new player, but from what I've seen the rebels seem to have a pretty solid squadron option in Jan Ors and some X-Wings. Jan allows any rebel bombers to bypass fighter screens with her intel ability, and paired with some generic X-Wings (who can use her brace tokens with impunity) she'll last a LONG time against fighter groups brought in to route her.
Here are my thoughts on a counter...
The Instigator Imperial Raider
The FFG FAQ states that Instigator's ability is unaffected by the 'Intel' keyword, therefore flying the Instigator within range 1 of any Jan Ors squadron ball may potentially stall or stop a bombing run completely. In addition to this the Raider I has an anti squadron battery of 2 black dice and can ignore Jan's X-Wing escorts. Jan will still have her braces (assuming she hasn't already exhausted one or both defending her escorts), but roll two raiders up onto the Jan ball and my thoughts are it might not last long. On top of that any brace tokens Jan discards defending herself can't be used to help out her escorts anymore.
I understand that you may be investing a lot of points into this counter (if you're using 2 raiders or the Instigator with an anti fighter force), and that investing this many points to just counter Jan might seem like a bit of a waste, but consider this alternative option:
Just bringing the Instigator by itself might be enough to stall the enemies bombers for 2-3 turns, and to me stopping 2-3 turns of bombing is worth the 48 points you'll be spending
What do you guys think?