Polino Khoroshko, from Port Vila in Vanuatu, was arrested at Hillberry Green after crossing during the second practice session on Tuesday.
Douglas courthouse was told she had broken a road closure order.
The 35-year-old, who the court heard had not been drinking and was very apologetic, was fined £1,500.
The hearing was told Ms Khoroshko was camping on the island, having travelled nearly 10,000 miles (16,000km) to watch the event.
It is illegal to enter the roads used for the TT during all practice sessions and the offical races, which begin on 1 June.
Hillberry Green is on the finishing straight of the 37.75-mile (60.7km) Mountain Course, at a point where riders can reach speeds of about 160 mph (260 km/h).
Practice for the annual event began on Sunday, after Saturday's session was cancelled due to poor weather conditions.
Speaking after the hearing, an Isle of Man Police spokesman said anyone who broke the road closure orders during the event would be "dealt with robustly".