I got similar advice in a similar situation in MA from all 5 atty's I consulted. Perhaps there is similar thinking on her atty's part - if in doubt she should definitely consult other atty.
My experience: MA is a fault state - but every atty said not to go there, judges hate A cases and it could backfire. There was no back and forth in my case he left on Dday and I had tons of email evidence, along with his written permission to be in his email.
Here is what the thinking was from my atty. Pre-filing - none of the support I received needed to be claimed as income. I was in the house, the bills were paid. Post-D... who knows...? Pre-filing - I was continuing to accrue interest in marital assets/pensions. I had health insurance. Waiting gave me time to set myself up better financially.
All five atty. said there was no advantage to filing first. So, seeing as the X was racing through one OW after another...I waited for the X to file - then counter-filed "cruel and abusive" in lieu of repeated promises of fidelity and repeated "womanizing".
It may have been more cathartic if I'd filed first, but financially life was going to be very difficult. During this time, I was reminded by a good friend that the pain wasn't going to stop just because I filed, or just because the D was final.
Not saying it was easy waiting for the shoe to drop and have XWH finally file - but none of this is easy. Both his atty and mine so it panning out the same way. 50% of marital assets, 50% of pension, and alimony. The one big difference I see - my X did not make "good money"... that might make a big difference... I don't know.