SAHP or anything else is irrelevant to jury service. It is considered something than any eligible adult in the UK should be prepared for. FWIW, I live in fear of being called.
I don't know about when a jury gets isolated, but for everything else you have virtually no chance of being excused. None at all. My husband managed to defer his first calling in the early 1990s, as he was a student nurse & it would have affected his studies. However, it was deferred and not cancelled.
As another poster said at the beginning of this thread, they too knew someone who deferred due to studies, but was called within weeks. My husband was never called again until March of this year - I don't think this was anything to do with him deferring almost 30 years earlier though. Maybe it was.
When he was called this year, the online forms were very detailed, and everything is spelled out clearly as to what you can and can't note down about your situation. The box where you have to input your work commitments, for example, requires explicit detail and gives examples of the exact things not to say, such as "my workplace is busy and there's no holiday cover". You really have to go in with the mindset that you can't get out of it.