I used eucalyptus and peppermint in pregnancy?

You are right that it is highly toxic. It's toxic to babies and adults and not recommended for use in pregnancy. However it is mostly only a risk if it is ingested. There is a small risk from using it on the skin but it isn't something you should let worry you. She washed it off and hopefully didn't ingest any. The heat it caused wouldn't be any kind of risk. Just keep an eye on her and if she feels fine then baby should be fine too. If however she does start to get cramps or feel ill then it's best to speak to your GP. Even then period like cramps are normal in early pregnancy so you still shouldn't panic.