I'll be visiting in May... what are some must-see/must-do things in Hannover?

I will be visiting my family for a few days in May. They will be working, so during the day I will have some time to kill!

I speak some German, but what are the local people's English like? I'm from Ireland and visiting with my mother who has no German....will she go missing? Haha

What are some things you'd recommend I see or do while I'm there? I love nature and animals, so it would be lovely to do something to cater to those interests, but I'm also interested in learning about different cultures.

I'm a vegetarian, so any restaurant recommendations would be lovely!

I'm considering going to Berlin for a day trip....would that be worth it?

Thank you! :)