Nothing is missing , we dont use " to do" with that verb.

I don't know if it's the same in all languages, but there's a clear difference in English between [try] [not to do] something' and '[not try] [to do] something'. In the first, you are negating the word 'think', and in the second you are negating the word 'try'. They don't have the same meaning at all. 'She tried not to think about ...' means that she made a determined effort to avoid thinking about something. She knew that this was an unpleasant thing to think about, so she mad an effort not to do this. She deliberately tried to keep these thoughts out of her mind, perhaps by forcing herself to think about other things. This is the meaning that the writer intended. 'She didn't try to think about it..' means that she didn't make an effort to think about this. You might use 'didn't try to think' in the following situation: 'The teacher knew that I was lying, so I didn't try to think of an excuse. I knew there'd be no point.' I hope that makes sense.

The second part of the sentence looks even weirder. I don't speak English as a first language, but isn't it incorrect? "She were to get caught" I would said something like - If she was going to get caught or If she was about to get caught, or if she gets caught. Nobody said something about the second part, and I have a question in my mind. Do I need to read a grammar book again?)

Gracias Camilo. Creo que es lo que contaba Su.Ki en su explicación. La partícula 'not' es para negar al verbo 'to think', y no al verbo 'tried'. Ahora lo veo claro. Muchas gracias.

Try + infinitive. Try to do something or try not to do something. Ella no intentó pensar is different from ella intentó no pensar.