Depends - if she's OT by BT you're probably better off going for the earlier BT as she may tack on at the end of the night, perhaps with another feed if necessary. If you push BT when she's already OT you run the risk of poor night sleep on top of that with an EW caused by the OT...
Why do you want to wake her after 1.5h of her naps? Is that to reduce the amount of day sleep? Another way to do it would be to focus on stretching A times (as gently as needed) but still allow 2h naps (for the first and second, at least if she'll take them that long) and this will result in BT getting later, ie a shorter night in total. But an 11h night is fine if it works for her, I've done even shorter (preferably no shorter than 10.5h IME) coming up to nap transitions. Better than a broken night!
The third nap doesn't necessarily have to be a CN just yet, it really depends on the LO. Since my LOs got OT quite easily I'd often end up with a longer third nap, especially with DS, who really needed to accrue a decent amount of A time overall before the night, but who got OT really easily if the A was too long, or the third nap too short. He was also a chronic short napper, so if he'd short napped earlier in the day then I found he could sometimes take a longer third nap and then manage a longer A time after it, which got BT to a better time for him. Does that make any sense at all? Sorry I'm rambling...