'Hennes' is technically correct as well, so I'll add it as an option, but beware that it changes the meaning of the sentence quite drastically from "She loves (her own) husband." to "She loves (some other woman's) husband".
'Sin' points the ownership back to the subject (She), while 'hennes' could point to any female.
The word "husbond" still exists, but it's mostly used when describing historical contexts.
Historically, "husbonden" wasn't just someone's husband, but the man in charge of the entire household, so on larger farms there may live several married couples (family, tenants, servants), but "husbonden" would be the the one who owned the farm and was married to its "husfrue".
You could talk about 'min samboer', which is a gender non-specific way of saying 'partner'. You could also use the word partner and be understood by most people (it takes 'en' in Norwegian), or 'min kjæreste' (girlfriend). And if you are married (marriage equality has existed in Norway for many years, remember), you could of course say 'min kone', which in my experience is more common in conversation than 'ektefelle' - but I'm not a native speaker, I just used to live in Norway.
I believe the s-possessive form emphasises that it is HER own husband, no matter which of those two alternative combinations you use. If you weren't emphasising it was her own husband, you'd use 'henne ektemann' and 'ektemannen hennes' instead - at least that's my understanding of it.