Hiya Helen,
I can hear how difficult that must be for you. And I know how frustrating it is when it seems like other people aren't doing anything! 
I can suggest a couple of people and organisations that might be able to help you and your mum. You may have heard of some of them:
- MIND - they work with people who are suffering from mental health problems, and (depending on what they've got in your area) can offer things like counselling, information, support or fun activities for your mum. You could have a look at http://www.mind.org.uk/Mind+in+your+area/, and see what's about in your area.
- Rethink - they do similar things to MIND, as well as run support groups across the UK. Those groups give people like your mum a chance to have a chat to other people who have similar feelings and experiences. That can be really helpful - it's sometimes difficult for people who haven't had your and your mum's experiences to understand what's happening, so it's nice to talk to someone who will understand! To find what's in your area, have a look at http://www.rethink.org/how_we_can_help/our_services/search_for.html
- Social Anxiety UK - if your mum really doesn't want to try those things, then there is Social Anxiety UK, who also do support and groups especially for people with social anxiety. They're at www.social-anxiety.org.uk, and you can find their groups at http://www.social-anxiety.org.uk/groups/list.htm
- Anxiety Care - they have a helpline on 020 8478 3400 (open every Monday and Wednesday 10am - 3pm) which your mum could call if she wanted some more support, but didn't want to leave the house. The website is http://www.anxietycare.org.uk/docs/home.asp
- I don't know if your mum might be interested, but there's some really good booklets about dealing with depression and social anxiety available here too: http://www.nnt.nhs.uk/mh/content.asp?PageName=selfhelp. A lot of people I've talked to have found these helpful in coming to terms with their feelings. Maybe your mum could have a read and see what she thinks?
The Royal College of Psychiatrists put together a leaflet about looking after your mum or dad, which you might also find helpful for yourself - that's at http://www.rcpsych.ac.uk/pdf/CaringaroundClock.pdf.
You wanted to know if you could ask for your mum to be put back in hospital - what's good is that there is nothing to stop you asking. Unfortunately, unless you're 18 or over, you don't have a legal right to make her cpn do that. If you're a person's nearest relative, and over 18, you can ask for them to go and see your mum, to decide whether she'd be better off in hospital. It is your mum's decision unless she was too ill to look after herself at all. If you ever feel that's what's happened, then call the cpn, or if it's out-of-hours, ring the police on 999. They will be able to take your mum to hospital, but only in an emergency. But let's go back to the positive...
What you can do is keep speaking to the cpn about how you feel, and what you're worried about with your mum. Though I'm sure you're very busy looking after your mum, it can be useful to keep a diary. It can help to write down how you're feeling, and how your mum seems from day to day. That also helps if you're trying to show the cpn that your mum has got worse/better - cos you can say exactly what happened each day! Depending on how your mum is, her cpn should listen to your worries. If there is anyone else who looks after, or sees your mum often, it might be an idea to speak to them too. If they're willing, they could come with you to see the cpn as well, to give her more of an idea of how your mum is.
I hope that's helpful - don't forget to look after yourself as well! The YC Net team can also point you in the right direction for support for yourself in your area.
Cheers,
Drew