ANSWER:
No problem in telling it to others after 3 months as usually the first trimester is crucial in a pregnancy. As for evil eye, if she maintains her daily adkhar, she would be protected from every evil by the grace of Allah.
PROTECTION:
You must maintain your 5 daily prayers on time without fail. Fix a time for reciting Qur’an everyday.
Maintain your daily adhkar of morning and evening, before going to bed, after every fard prayer, while entering the washroom, while going out of the house, before eating etc and this will act as a shield against everything evil with the Mercy of Allah. You will find these duas in a booklet called ‘Hisnul Muslim’ or ‘Fortress of the Muslim.’