What does she like to do?
Paperchase sells a happiness journal aimed at teens that you can write in to help you find out more about yourself - what makes you happy and sad, what you enjoy doing, etc. That might give her some ideas.
What about something creative - writing, cartooning, crafts, gardening, colouring in?
Volunteering - with the elderly, in a charity shop, with a nature group? To make her see the bigger picture and see she belongs and can be useful/helpful
Wellbeing apps - some good ones listed here:
www.theguardian.com/lifeandstyle/2014/jun/21/happy-life-
best-psychology-apps
Getting out and about - seeing new places fires up new synapes in your brain. Whether you go for a wlak in the woods or to a new town for the day, it works
See a funny film together
Sports
Guides/Scouts
Is she having counselling for her depression? I'd also ensure she limits mobile phone/social media use, as this can make depression worse, esp. in teens.
Make sure she spends time with the family in the eves and at weekends, not up in her room alone. Play board games/cards/chat/cuddle on the sofa and watch a film.
Also if she watches the news, she should stop - too much news makes my teen sad.