having to extend naps with shh/pat and taking about 15-20 min to settle for naps.
It might be that you'll still have to do this even with the right A time. I know it's hard to figure out, but since she's waking up at 45 minutes no matter what, I think it's just a matter of getting her through the light phase of the sleep cycle. It might be that you'll have to do this every nap for a while (that's what we had to do). It's a developmental thing starting around 3 months and it usually rights itself by 6 months--not saying it can't happen sooner than that! I just want you to know that if no matter what you try, she wakes at 45 minutes, it could just be developmental. 15-20 minutes isn't horrible to get her back to sleep; keep at it for a couple more days and see how she does
So for length of naps, wake for regular feeding time even if nap goes longer than 1.5 hours because of shortened nap and activity time in the previous cycle?
It's hard to give a definitive answer for this, just because the scenarios could differ for every short nap. If she has a shortened A time due to the previous nap being short, then let that next nap go no more than 2 hours, or only ~15 minutes past the next E time. That's just my general rule of thumb.
