I thought it was The Death of Mrs Westaway, by Ruth Ware, but it's not. Similar plot, woman inherits house from distant relative she knew nothing about and moves into it. I thought it was set in Cornwall, but maybe not. It's remote, maybe in the woods? There's a slightly creepy neighbour, I'm fairly certain the house has no power and is really run down. I vaguely remember a scene where she leaves her rucksack in the kitchen and it's not there when she comes back. And maybe something to do with a dead bird?!
I read it fairly recently, within the last 6 years and it's probably a fairly new book (within the last 10-15 years I'd say) I love Cara Hunter, Lisa Jewell, Ruth Ware, CL Taylor etc so will be similar to work from those authors. It's driving me cuckoo. Please help me!!