Long-term experimentation shows that, at least as long as she's not getting bloodily injured in regular fights with Los Angeles's demon population (and she can generally make it through unscathed, and now every supernatural creature in this hemisphere knows that the Slayer can set you on fire with her mind and some demons keel over with no visible injuries if she just looks at them), she can operate in fine and suitably Slayery condition while being nibbled on most days. It would probably not be a wise exercise for Sherlock to attempt to subsist solely on her, though, so the brick house does acquire a fridge and a microwave thanks to Sherlock's slightly stolen inheritance.
This afternoon, Bella is sitting in an armchair in the house that is Jarvis, reading about some neutral demon species and taking dutiful notes.
[Oh, great. Maybe there's a nest of them in the library or something camping out on the Hellmouth.]
[Not really. This creature doesn't care that the Slayer is chasing it. I'm not looking forward to meeting twelve of it.]
[Giles,] says Bella, when it's clear that this is in fact where the creature is going, [it's headed for the school. Probably the Hellmouth.]
[Have you been in the library lately or do you take summers completely off - do we know how long a nest of 'em could have been sitting there?]
[Okay. Considering tackling it before it gets there, so I can see how tough one is alone instead of seeing how tough twelve of it is.]
[Not a strong reason. It just seems like it's in a hurry, and it's ignoring me, even though I'm right behind it - if I were it, I'd fight me, unless I was going someplace that was better ground for me to fight in.]
[Sherlock, opinions on engaging it now before it introduces us to any friends it may have?]
[I can't see you, but are you keeping up well enough, can you cross its path - we'll see if it reacts, go from there?]
[Shit, are you okay -] Bella makes a jump for it and manages to land on its back. It doesn't seem to care. It doesn't slow down.
[I am less certain that engaging is wise,] he says, but he picks himself up off the ground and chases after them both.
She swings around its shoulders to try from another angle.
It grabs her off of it, hurls her to the ground, and steps on her in its unslowed quest for the school.
She doesn't move.
"Hello?" Charlie says to the phone.
"Bella has encountered some trouble. She is alive, and will almost certainly be fine, but she needs to be taken to the hospital. Please arrange for an ambulance at Chester and Oak; you can most likely prompt faster reaction than I."
He sets the handset of the landline down on the counter and radios for an ambulance, barking orders at the paramedics.
When it's on his way, he picks up the phone again. "Who are you and what happened to my daughter?"
"My name is Jarvis. She ran afoul of a Sunnydale hazard, which has since been neutralized."