Do you have a UV light/torch? Just wondering about the possibility of ringworm which can just look to the naked eye like bald patches, however ringworm glows under UV light -a specialist guinea vet taught me this when I had a baby pig who very quickly developed random bald patches (I thought she had been assaulted by the others - it was, as you describe - she lost patches of fur really quickly). If it is ringworm this vet told me that it can be a sign of a weakened immune system response sometimes brought on by stress. If it is ringworm, it is really easy to treat with prescribed medication (Sporanox suspension in the UK) - which, according to Poppy, tastes really nice - she would lap up her syringed dose - not like Baytril at all!
There is also the possibility of selnick mites which you can usually see around the belly area. I had a case of that years ago when I got some wood chips from a not very good pet store. Again, that is very treatable but you would probably see little dark/reddish dots in the bald patches.
Do you think that she is feeling stressed? In my experience when it comes to pulling their own fur out due to stress, they tend to pull it out on their wrists. I adopted two pigs from a very large herd last year (I wish I could’ve adopted more of them!). One had obviously been very badly bullied and thankfully she is not doing this anymore but it has taken her a while - piggie version of biting finger nails I guess.
Sorry for the waffle, I’m sure she will be fine after her trip to the vet