We hear from a lot of parents who are worried about their young people at this age- you're definitely not alone, and it's really great to see that you've both been able to connect here.
The disruptions of COVID have also had a pretty huge impact on young people, especially when it comes to connecting with their friends online/ via their phones, rather than in person - and as a parent, it can be hard to know what behaviour is normal, teenage stuff- and what behaviour is something to be concerned about. I know that my daughter (who's 12, so just at the beginning of the teen rollercoaster!) has definitely been spending more time in her room lately, and more time on screens than we used to be comfortable with - we're currently in lockdown, so part of that is unavoidable.
To some extent, it's quite normal for young people to want to connect with their friendship group, rather than their parents, as they move through adolescence- but it's also important for parents to know what behaviours might be a sign that something's not going so well with their mental health.
In general, if you see a sudden change in your child's behaviour, or they stop doing activities that used to bring them joy, if they have trouble sleeping or are suddenly sleeping much more than normal, or if your gut feeling is that something just isn't "right" with them- it may be time to have a chat with them to see if they are OK. As a parent, you know your child best- though I also definitely acknowledge that it's sometimes also really hard to know what is regular teenage moodiness, and what is a sign of something more !
We do hear this question a lot from parents, and we've worked with psychologists as well as parents to develop a few guides to help parents:
This video is with a psychologist who talks about how to know when your teen needs professional help
This quiz helps parents to work out what type of help might be the best fit for you and your teen
And this is a list of other articles and resources all about how to get teens help, if they do need it
I hope that some of those are helpful for you both- I know that those conversations can also be really tricky to have! Some great advice another parent gave me once was to have those chats while you're doing something with your teen- and I know it's worked really well for me. I find my daughter is much more likely to open up to me when we're doing something together, like going for a drive, having a walk, or even doing the washing up- for some reason it feels much less pressured/ forced.
Wishing you both the best- keep us posted about how you and your daughters are getting on. It can definitely help to vent sometimes- you're not alone, and this is a really safe place to vent/ get advice 
