and vastly different lifespans.
Why does everyone always get hung on this, as if real mortal people couples somehow magically perished simultaneously and didn't have to cope with grief just the same?
A lot of it is that humans have roughly the same lifespan so they can generally have one lifelong partner and be old when they die, stay celibate until their own death or at most have one remarriage after becoming a widow(er).
If two types of beings have radically different lifespans then the older lived one either grieve their short-lived lover for most of their life or get so many serious lovers that it's highly debatable how "serious" the longer-lived being is about them and if they are not just short flings that only the short-lived partners are deceived into thinking is the love story of a lifetime.
For me, the issue is more about aging. The maid will slowly grow older and less capable while the vampire stays exactly the same, both of them forced to watch as their lover drifts further and further away while still remaining at their side. It's like a romance where one partner is guaranteed to suffer from a progressively debilitating illness, but where said illness wouldn't be an issue if they dated someone else.
typically vampirisation is supposed to take place only if you are killed by a vampire bite
I've heard that you can only become a vampire if, after they drink your blood, you drink their blood. You usually drink it from the wrist. You exchange blood basically.
It's appeared in most stories I've read about vampires, and maybe it's the case here.
So, the maid should be fine. :)
It depends pretty heavily on what version of vampires you're dealing with. Some require you to drink their blood, others just require them to drink yours or even just take a single bite. There are also versions where its dependent on some quality in the mortal, rather than a specific action, or completely disconnected from the vampire (possibly requiring some sort of ritual or practice).
As with any fictional species, the specifics are determined by the author and little else.