I always have at least 1 backup. 2 backups if I'm travelling a long way (I will also usually bring my laptop in case I want to search the local area if all my backups go to shit.)
I regularly saw another well reviewed WG in London who specialised in DT, VFM, submissive and allowed filming (now retired). Your review is pretty much word for word for what happened to me once with that WG. I was driving and picked her up after waiting for like an hour. Also there was the intermittent texts that would imply she's nearby / on her way but wouldn't give any detail on time of arrival etc. This WG was known to have a drug habit. 90% of the time you would wait min 30mins, but it was usually longer, she was always worth the wait imo. Of the say 15 times I saw her, she only bailed once but at the same time I must have waited for at least 8 to 10 hours combined for the other meets.
No one should ever give a deposit unless it is a very small amount, Lou sounds like she is at the start of having a problem, which means her meets are necessary for her to score, if you give a deposit, she can then score before she meets you, once she has then the meet is not a priority anymore and even if you do meet, if she is still high she won't be fun to be around.
Also always drive with a WG that's unreliable as you have the flex to relax, go grab some food, bail, or drive to another WG. With public transport you will be fucked and get annoyed as hell waiting around nearby the location.
She sounds like a nice girl and is probably genuine in her apologies. I am only theorising, she may not have any issues with drugs at all and is just very unreliable.
I will see her regardless of her negs.