Blood in the back seat of the car would also be normal if she was gang-raped by all three.
The hardest evidence at hand seems to be --
1. she was intoxicated at Carlos and Charlies
2. the Dutch kid was in a shoving match with some of her fellow students
3. she left with the Dutch kid and his Indian friends in a Civic
4. she was kissing with the Dutch kid in the back seat while they were parked by the beach
5. she never got back to the hotel
6. there is blood in the back of the Civic
And admittedly, some of the above is not really hard evidence at this time, since it is hearsay from defense attorneys and other dubious sources.
At this time we don't know whether she got drunk by herself or someone slipped a Roofie into her drink.
The blood might be from her period, a broken hymen, vaginal abrasion, a bloody nose, a bite, a cut, ... However, I don't think that strangulation generally results in blood.
If the blood was from sex, the sex may have been consensual or not, or it may have started out to be consensual with the first one and not the others.
She might be dead, or she might not. The authorities have not said, at least not officially.