Whilst we know that Hollywood is a dark, dark place for children, we need to be a bit careful putting two and two together and making five. She had giardia which is transmitted through ingesting infected faeces and can therefore be transmitted through unprotected oral/anal (‘ass to mouth’ - sorry!) sex but can also be transmitted through contact with infected animals, infected soil or ‘infected’ water. This type of water isn’t just present in the developing world. She could have had a pet that was infected or have swam in a lake which had giardia present and inadvertently swallowed some of the water. She couldve been infected by someone else’s poor hygiene. She could have eaten vegetables/salads that weren’t washed and ingested it that way. According to the CDC, giardia is the most common intestinal parasite in the USA. Children in childcare settings and children in nappies are most at risk of infection.
Basically, anal-oral sex is a risk factor for giardiasis but it is by no means the only means of transmission and it isn’t the most likely in a young child, who are themselves a population at risk of the condition.