That is the same problem I went through. I bought my wife a new helmet and now she does quite well. She had an open face and I bought her a flip up full face helmet. Seems like there is always more upgrades to pour our fun money into. Hope that solves your wind problem and you can have a great working intercom system.The biggest problem we have so far is that her helmet is so noisy, that we effectively can't talk on windy days, or on the highway.
More accurately, I can hear her just fine, but she has so much wind noise getting in that she can't understand me.
I haven't found a good solution for that yet. On my Shoei I can install the chin curtain and instantly, way less noise, Her helmet is a Bilt Fusion, which unfortunately is not designed to accept a chin curtain.
I am not going to waste $15 on one of those neoprene neck sock contraptions. The reviews say they are flimsy and don't stay in place well, plus as the weather warms up, they seem like a ticket to Heatstroke City.
Getting a helmet with more features may be the only fix. Unfortunate, but we only paid $60 for the Bilt, so not a huge loss.