I'll do what I can to answer some of your questions
1. Do you think this is 18 month SR?
Yes it could certainly be. Can't say for sure of course. Part of the 18 month regression is that teething is often on and off around this time and you can't really know for sure that teething isn't playing a part, the 2nd year molars can be moving for ever before they finally come through (I had a year of non-stop teething pain here, only 3 days rest between the canines and the molars, those 3 days were bliss! ...and really showed that an independent sleeper really just wants to be asleep, when they are in pain they just cannot do it, no amount of help is too much IMO). Another aspect of the 18 month regression is a big language leap, I do remember that (around 18 and 21 months), terrible sleep and then suddenly new words pop out. Yet another aspect is that around birthday and half birthday (so 2, 2.5, 3, 3.5 etc) sleep and mood often goes crazy, there is nothing to 'fix' it, only to know you are not the only one with a child who goes through it and to be as calm and patient as possible.
2. How do we deal with her crying in middle of night as nothing seems to help??
Through teething, illness, developmental leap or half birthdays there isn't much you can do to make her calm or make her sleep, all you can really do is be there for her. It may appear that patting doesn't help but knowing you are there with her means a lot to her. I'd probably set up a comfy chair in the room, pick her up and have a cuddle for as long as it takes. If you're dealing with 1hr+ and suspect it will continue I'd be tempted to prepare a flask of tea for the night shift. If it is super bad I would probably take her out of the room for a little while and see if she'll calm. Mine has only come back downstairs after BT maybe 4 or 5 times in his life but during teething there was literally nothing could be done other than to distract him from his pain with cuddles and low key (calm) kids TV which I'd pre-recorded. It's absolutely not something I'd do every night but it helped here on the very worst of the teething times.
Sometimes I took mine out of his room and just went and sat on my bed, the change in location seemed to help him calm down.
3. I don't want patting to become a prop
I wouldn't worry about patting being a prop. The amount of NW you have and the length of them means there is *something* going on which she needs support through. Tweaking times on your day routine may help with the patting at nap time.
4. When she is upset and crying at BT we go in and sit with her and pat if needed until calm or until asleep if really upset. Is this ok or do we do something else?
I seem to have a memory of lots of BWers saying they had taken their LOs into their own bed during the 18 month regression. I might have done it myself a few nights (I'm trying to remember if it was the 18 month regression, think it must have been), the regression is such a crazy time, it's like all bets are off. I didn't take mine into my own bed as a matter of course, but more like a few times when things were really bad. They need a lot of comfort.
But, yes it's ok to sit with her and pat her.
5. If she does manage to sleep through her nap it is not more than 1.5 hrs, only if she wakes in middle and I have to pat her to sleep again I can get her to sleep around 2 hrs by sitting there in case she starts waking again, which is really not fun! How do I get her to nap 2 hrs or might this never happen?
Maybe 1.5 hrs is just her natural sleep time.
7. Do you think I need to increase A in morning?
I would set the nap time regardless of what time she wakes. Usually LOs over 1yo and on one nap do better on a set nap time.
I think I'd try to reduce the last A time though, has she always done a longer A time to BT or is this because of where her nap is??
With an 11 to 11.5 hr night she needs to be going to bed more like 7.30pm really for a 6.30/7am WU, in which case the nap needs to move much later to prevent an even longer A time to bed...unless as I say she's always preferred a super long A to BT.
Maybe:
WU 6.30/7
(roughly 6hr)
nap 1.00 - 2.30
(roughly 5hr)
BT 7.30
What do you think? You know her best