DH's half sister, older than him, same DM, different DF. I'll refer to her as CFSil henceforth...
We grew up in the same street, CFSil would sometimes visit from London so I knew her kids as did a few of us as they were often out with my now DH (we were just friends back then but I had a major crush on him!). When his DF died, his DM fucked off with some bloke within a few weeks, leaving DH to fend for himself aged around 16 in a 3 bedroom house. No surprise that he suddenly got lots more friends and got into drugs but that's another story!
CFSil decided to go and stay with him to 'look after' him but it was obvious from the outset that she was there for her own benefit and definitely not his. Looking back, she was probably running away from debt... She was always running up debts in other people's names and years later it came out that she managed to forge her own mothers signature and spent all of DH's inheritance and the rest of what DMil had in the bank. We still don't know how much but we're talking tens of thousands at least. Nowadays it never would have happened, how she wasn't arrested is beyond me. DMil never did take any action and continued to 'let her off' throughout her later years when she continuously ran up even more debt in her name. We looked into financial abuse but without DMil's agreement there was nothing we could do. Sadly DMil passed away a few years ago...
Anyway, CFSil once hired a number of TV's from radio rentals back in the 80's/90's but never made any payments on them. Obviously radio rentals came knocking to enquire about payments or take the TV's back. Turns out she had put them in her DF's name so when they came, she told them he had died and somehow convinced them to let her keep them. He was alive and well (and no doubt oblivious to all of this) for many years later.
When I was a teenager, I used to babysit for her 3 DC's 2 or 3 nights a week while she was at work, but she never paid me a penny - I was young and extremely naive of course. She did once give me a pair of jeans that I liked though... 
She invited herself to our wedding - we were going to just have parents & kids, small affair, no chance of that. After we married, she would invite her youngest DD & DS to stay with us for the weekend every now and then, somehow I always ended up having to do the journey (about an hour). It was OK when my DC's were having their weekend at their Dad's but I struggled to feed them all when we were all together. If I could have afforded it, it wouldn't be an issue at all but I was working part time and DH had only just moved into the area (to marry me!) so he wasn't working yet. You can't put a price on family though so I didn't say anything. Then she asked if DN (11yrs) could come and stay for 'a few days in the holidays' so we agreed but on the basis that a contribution was made to food and that she came to pick her up as I kept getting migraines from all the driving. All was agreed but instead of providing the contribution to food, she sent a few bags of cheap junk food that none of us liked, not even DN! We took her with us for days out with DC's, all sorts of summer activities and included her, she was family after all. I didn't like the way she spoke to my DC's and told her so, firmly but she was only 11 so I didn't take it too seriously. During the first week, we were shopping for something for dinner when DN asked if she could have a canned meal (not something we would usually have bought but she convinced us she really wanted it). Got home, opened the can, she didn't like it. Fair enough but I wasn't letting a child under my roof go hungry and it was pay day so I insisted we went to McDonalds or KFC drive through to make sure she had eaten.
By the second weekend, we had all had enough but CFSil had put off coming to collect her three times so I said we would be bringing her home on the Saturday, regardless. We arrived as agreed but CFSil wasn't there, she was out having her nails done and insisted that we leave DN home alone as she had a key and CFSil would be home soon. It took me a long time to get over the fact that we left her alone that day - we had to get back for my DC's. We did wait about an hour or so before finding out that DN had a key... A week later, we receive a phone call from DMil to say that CFSil is furious we hadn't fed DN and that I was stroppy and shouted at her too much (I wasn't a shouter back then, I've since grown a spine though!). Apparently we made her actually starve on more than one occasion
despite having done the opposite 
There are many more stories of her unbelievable cheeky fuckery towards so many people. We've had nothing to do with her since DMil's funeral. DH purposefully gave her his wrong mobile number so she couldn't harass us. Such a shame as we adored the kids and they had to put up with so much more than us. I'm a forgiving person but have learnt that it's just not worth it with her, she always has an agenda and is toxic. In some ways, I thank her because I've learnt from it and have spotted CF's coming a mile off and therefore been more than equipped to say NO , end of. Wow, this is cathartic!