I don't know about the facial palsy, but it's worth saying that SIBO can eventually cause vitamin deficiencies, including B12 and folate. Healthy people have bodily stores of B12 that can last several years before deficiency sets in, but if the levels were low to begin with, SIBO could theoretically hasten exhaustion of them. People may also harbour bacterial overgrowth for a time without clear symptoms, so the condition can have been present for longer than realised.
I know from experience that if it's left untreated long enough, B12 deficiency can cause very unpleasant neurological effects, including loss of memory and skills to an extent that resembles dementia. The symptoms may show up as an easily recognisable pattern in some cases, but in others it's harder to diagnose because only one or two rather non-specific symptoms are present. The neurological effects are reversible, but permanent damage is a risk in the very long term.
Bear in mind that if she started supplementing vitamins before any blood tests were done, it would throw the results—wherever possible, it's better to test first.
Good luck with getting support for her, it must be horribly worrying.