I'd ask a CA attorney if there is any "strict liability" is involved. This isn’t sky-diving: she was paid by TT, not the other way around. Otherwise she has to meet the low threshold for civil cases. I'd say TT needs to hire a really good attorney right now, and be ready to swallow his pride and take a good settlement if he can get one.

Anyone else who shot scenes with her, even without Darren, should probably erase (not just delete) everything, right now. It's too late if you wait to see if her lawyer is interested. I mean masters, bloopers, cutting-room fragments, notes, paperwork – everything you aren’t required to retain by law. You want nothing a motivated lawyer might twist into showing she was placed at risk, even innocent-seeming director's instructions.

Make notes of every bit of evidence there is of Lara hooking, especially names and dates. If it gets into an effort to show she probably got HIV on a given shoot every bit helps to show she may have got it elsewhere too. This may not matter for TT but may for anyone else.

Finally general rules:

1. Incorporate everything. Never do any business personally, always through a corporation. Never mix roles of corporate entities.
2. Carry general business liability insurance. This probably isn’t easy to get for porn but without it the corporation probably doesn’t work.
3. Don’t leave extra cash in the corporation. Take the tax hit and pay it out. Between government and lawyer risk leaving money in the company is too risky.

As for “Can you sue for that”: my dad was an attorney and his usual reply was “You never know you can’t until you try, and you aren’t sure until you’ve tried a few times.”