Partner Has Been Denied Entry To US ESTA At Departure Airport, ESTA now revoked - What Are Our Options?

Hello. My partner, Italian national, has recently departed US to see her relatives, expecting to come back to me last week. Round trip tickets were booked so that she would stay less than 90 days in the US - we were always following 90 day limitations (she traveled to US and back multiple times in past 2 years, never a problem)

She was able to check in, submit US entry forms and IDs and go through customs, however at the boarding someone from airline (British Airlines) called her to the booth then told her someone must speak with her on the phone. The person, never identified who that was or what was formal role, asked her couple questions about travel, who and where she will live with during her stay (with me obviously) then very bluntly told her she is not allowed to board. Didn't give formal reasons or anything, hanging up. Same individual then called airline crew at the boarding stand and apparently ordered them the same.

We were always respectful of ESTA regulations, never overstaying 90day limit, strictly no work or business activities on her behalf in US. Both of us are in mid 30s, zero criminal or admin records, with well endowed career and healthy income.

Later that day, she checked her ETSA status and it was now revoked. My partner, smitten, then tried to petition for B2 visa, filed application, fees and passed all automated checks. At the interview, staff was surprised she got called at before even leaving Italian soil, asked her to wait while checking something then claimed she overstayed by 1 day in 2024 (it's not true, I managed all the bookings and have US entry and departure flight check-ins to prove it) and because of that B2 was also denied.

When she got her passport back they also handed her denial letter that mentioned nothing of the above only that she is being denied because they don't belive she will come back to home state after visa expires.

Apologies for long back stories. What I'd like to understand is,

What are the chances to get second B2 interview and get approved having shown proof that she never overstood 90 days? Or at this point it's just frivolous claim made out of the blue to meet some kind of denial quota?

What/who can answer if there are any formal bars or restrictions against her name in the system (again at this time we have no A# or any case tracking ever given by US Customs or embassy)

We eventually want to intimate K1, what are if any issues that this situation can trigger for when K1 process starts?