The 15 mins increments are just making her more and more OT and taking away from her sleep
This is what happened with mine too. Every night he lost another 15 mins so over time it ended up quite a lot of sleep lost. He had a very strong body clock waking him regardless of the later BT.
So should i leave it a fewa days after the clock change or straight away.
As the clock change doesn't actually effect her routine, just make your times better (result!) there is no harm in doing it all at once it's just that if it was me I'd like to sort out the clock change first and then move the routine so that I knew what time I was working to. I also need to write stuff like that down to make sure I get the times right!
Clock change will hipefully get us to BT 18:30
from your eASY above it looks more like clock change will get you to 6.45/7.10 BT rather than 6.30...but yes
Night 1 BT 19:00
Night 2 BT 19:30
Night 3 BT 20:00
yes that's it. If with clock change you are actually already close to 7pm you might need to go further than 8pm, possibly 8.30pm for a day or two unless she wakes later before you reach that.
Do you think 3 days will do it, also was it just an extra quiet 30mins
I would also move meal times the 30 mins as these routine times help LO to know where they are up to in the day. The more you can move to the 'new' time in the routine the better, so also bath and any other routine things, move them all the 30 mins to give her body clock a good indication of where she is at.
Then how quick do you bring BT
Once you get a later WU, I mean properly later, 7am or later, then that day do the same BT you already did (whatever it was) just to make sure you don't slip backwards too quickly. Then the next day make BT 15 mins earlier, watch what time WU is. If it is still good, past 7am then that day bring BT another 15 mins earlier. As you are not capping the night sleep she 'should' be able to get as much sleep as needed once her body clock lets her sleep past 5/6am ish.
I must warn you - it's all guess work - it worked for my DS, I was willing and prepared for the worst (ie OT NWs) but it worked out much better than I expected.
Good luck!