Can she incorporate an LLC and have the company hire the LLC? It's the same net cost to the company. Then she can open a solo 401k, which allows for huge contributions, plus an HSA. If she gets to control show she's paid, I'd go that route in a heartbeat.
You say it's 5500 gross plus a raise of $1400. That 5500 gross is more like 6400 to the company (spitballing, NYC may have special taxes, plus it's a European company so who knows what kinds of taxes they pay at home on her labor), so with the raise, the total cost to the company is in the zone of $8K month for her labor. If she got paid a flat 8K/month on a 1099, she's at 96K for the year. Per a solo 401k, she could contribute 25% to her own 401K as the employer (~24K) and ~19K as the employee, for a total tax deferral of $43K ish per year. Then if she does an HSA and expenses a bunch of things, she can further reduce taxable.
The shortest route to FI, imo, involves a solo 401k.