Okay, I'm going to focus on character closeness since you say this is what you're struggling with and it's also probably what I'm reasonably good at. Be warned, I have teeth.
Okay, I think grammar and everything is good, and the bases are here. I just think it needs to get into the character's head a little more. Hopefully some of the comments are helpful - if not disregard.
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Charlie brushed the last few pieces of dirt away from the skull. From her kneeling position, she rocked back onto her feet to admire her handiwork. Although it could be long and laborious, this was her favourite part of the job and this specimen had the potential of being a particularly interesting case. She reached over and moved her finds tray nearer before picking up the cranial fragments. As her fingers wrapped around the first piece she felt a jolt, and then darkness.
I think it's not a bad start at all. Reasonably close for a character we don't know. A bit more about how things feel might bring it alive - is that first piece hard, cold, just fitting into her hand? that sort of thing.
Inhaling deeply, she almost choked. Dung. which smells like? Does it turn her stomach? After a more tentative breath, through her nostrils to provide some filtrationthe key to close character work is to try to make thoughts think what a person really does. She's fallen through a portal (see comment below, on first read this didn't come across to me) and yet she's thinking of how breathing can increase her filtration? would that really be what you'd think. Or would you be in a panic, thoughts whirling, trying to make sense of things? she determined more than one type of dung. Ears straining, she tried to find familiar and reassuring noises: the constant throng of traffic, the wail of distant sirens and the cacophony of people talking, but the only sounds were bird song, rustling leaves and moving animals. That explains the stench, she thought.I'm a bit lost - how does the absence of noises tell her anything about the stench?
“Are you alright?” a female voice called out from a distance.
“I think so.” Charlie stood. brushing herself off, maybe? Seeing actions keeps us close, provided you don't overdo it. “Where am I?” She spun a full three hundred and sixty degrees to take in the scenenice place to tell us what the scene was. Here, you're losing me, but looking up I can tell she's portalled, or something. I think make that clearer the paragraph above (unless it's only me who didn't quite grasp it). “I-I don’t understand.” To add to her confusion, she realised that the words coming out of her mouth were not English, not that she had any idea what language they were.
“Have you banged your head? Come to the house and Ma will attend you,” shouted the stranger as she hobbled up the field towards her.Okay, so here she has seen the stranger. Tell us if it's a woman or a girl here, not later. Keep us with her as she sees and does things.
Charlie looked beyond the girl, who appeared to be in her late teens, to the house. Her mouth fell open. This must be a joke.
She grinnedwould she? I'd be in rather more of a panic than this as she looked around. “Am I on one of those candid camera type shows?” Her smile soon dissipated at the girl’s blank face.
“You use funny words. You’re not talking sense. I really think you need to be looked over. I can get Kael to visit.”
The girl walked towards the house but Charlie found herself rooted to the spot, mouth agog. Although she had no idea what words this stranger was saying, Charlie understood every one. The teenager doubled back and with a hand on her elbow guided her across the field.
“You’re not from these parts are you?” asked the girl. “I know everyone who lives around here and I’ve not seen you before. What are you doing here?”
“Er, no I can’t say I am from here.” Charlie swallowed her nerves. “Where is here exactly? My name’s Charlie, by the way.”
I agree that this needs to be much, much closer. How do those nerves feel? What's going through her mind? Try acting the scene out - what would you do? Try to get back? Try to find another way back? But you wouldn't wander over to a house with a stranger, surely? I wouldn't. Not until I was convinced I had no option.
“Charlie? I’ve not heard that name. You must be from Verulamium. Those Romans have strange new ways.” ‘Romans’ was said with such venom Charlie was surprised she hadn’t physically spat. “What are you doing here?” Her tone hardened as she repeated the question.
“I, er, I got lost and wandered into your field. How's that voice sounding? Scared? Choking? How's she feeling? Please don’t think I’m a threat. I’m really not. I’m so confused as to where I am.”
“I’m Isoldaso, she's suspicious and wary of Romans, who she thinks Charlie might be, yet she's giving her name and her ownership of the farm?,” said the girl as she looked Charlie up and down with narrow eyes, “and this is my family’s farm. It takes the first portion of the sun’s journey to walk to the nearest village and back, and Verulamium is about a whole sun’s walk away, but you must know that, otherwise how did you get here?”
Okay, I think grammar and everything is good, and the bases are here. I just think it needs to get into the character's head a little more. Hopefully some of the comments are helpful - if not disregard.