Hello!
I am doing well, thank you - hope you are too!
First of all, huge congratulations on the VS offer!! In terms of the situation, I would say that you have handled it well so far by flagging it to Firm B at the AC.
I would send a short and polite email to Firm B either this evening or first thing tomorrow morning - it is unlikely that they will view this as pushy, as they understand that you have a deadline and are simply enquiring on whether they are able to provide an update. It helps to keep it brief and factual - you could reiterate your strong interest, re-mention the expiring offer, and ask if they could give any indication of timing.
If needed, you might be able to ask Firm A for a brief extension - firms are used to these kinds of requests, and even if they can't grant the extension, they won't view it negatively!
I hope you are able to get a response soon, and congratulations again!