I had times when i texted agencies and didn't specify duration, sometimes they would ask, but most would not, as they are either used to me booking 1h or they consider unless stated otherwise that 1h is the standard. Now if you say you met her 6 times and 5 out of those 6 were 90m, she likely assumed it would be 90m. Why not reconfirm with her the duration, that way you will be sure.
I don't understand what "reg flag/danger" there could be if you sure you are really in contact with the right person. Worst than can happen is she ghost you... wich sure would suck, but thats why Plan B are important. But no an indy escort won't show up at your hotel with 2 big guys and try to rob you... lol. If these set ups may happen, they always happen in incall where they have "home advantage".
Just be aware that "i forget something in the car" is 98% of the time "i won't be back, you just got robbed". So if you pay in advance, if that was to happen, ask her to give back the payment. And don't accept a purse as "deposit" as i read in the past they would have no problem losing a cheap purse they probably paid 2$ at goodwill with a pack of smoke almost empty and a couple kleenex
But seriously if you seen her already multiple times, i don't see why she would do anything shady. She probably want to keep you as client...