germs - advice and support

I think I was about her age or a bit younger when I suddenly got very obsessive about a specific disease/worm as well. My sister also went through a similar thing but more extreme/about different things.
We both still struggle, but it affects our lives a lot less now. What helped us:

• ‘giving in’- while not technically recommended as it can make it worse, in both our cases being able to take measures that alleviated the worry about [triggers] allowed the anxiety to subside a bit, so we could then start to actually work through the issue. We went through a LOT of antibacterial spray for a few years…
• Knowledge- neurodivergent brains process a lot of information. Uncertainty can lead to anxiety, and while knowing too much can also lead to developing new fears (this was my problem), my sister found that certain bits of information she hadn’t known before helped her cope with the worries better. For example, (approaching this with a therapist is wise) learning a bit about the immune system and how they destroy germs, ‘beneficial’/non-harmful microorganisms (although I’d skip the bit about resident bacteria for now) and how many different lengths the body goes to to keep itself safe can help. 
• Exposure- WITH a therapist/after the anxiety is reduced- this is the last step really, but positive interactions where she’s not worrying about germs really help. Riding for the Disabled Association would be my recommendation, horses are great because they’re ‘dirty’ without being associated with germs in the same way.

A problem like this is multifaceted- is your daughters worry about getting sick? That might be a part of a wider issue surrounding energy levels/coping skills/body awareness. It can also be a sensory issue- I categorise door knobs as ‘germy’ but this is more because of the feeling they leave on your hands (I HATE the feeling of metal, so metal doorknobs = bad feeling on hands = same feeling as doing something germy [therefore] doorknobs = germy). 
I’ll ask my sister if there’s anything else she can think of to help. Good luck to you both.

To add to the first point, looking back a lot of it was about control- not in a malicious way, but if she’s used to coping a lot with stress and not necessarily showing it, this can be a way her brain is trying to regulate. Things like a schedule she can have control over or ’her own’ cleaning supplies can help this and means you can start to address the problem without having to actually talk about it (which she likely just isn’t able to cope with/communicate her feelings well enough for- even if she seems good at communicating most of the time).

To add to the first point, looking back a lot of it was about control- not in a malicious way, but if she’s used to coping a lot with stress and not necessarily showing it, this can be a way her brain is trying to regulate. Things like a schedule she can have control over or ’her own’ cleaning supplies can help this and means you can start to address the problem without having to actually talk about it (which she likely just isn’t able to cope with/communicate her feelings well enough for- even if she seems good at communicating most of the time).