Yes, definitely time for routine adjustments
. At 5.5m many babies are already beginning (or even well into) the 3-2 nap transition and would be consolidating their 4h EASY (two long naps and a CN) into two long naps.
Your LOs A times are really tiny for 5.5mo, there's no wonder she's having trouble settling at bedtime. She just isn't tired enough because she hasn't had enough awake time. I would suggest:
Start with the first A of the day, next 3 days add 10 mins to it so she is doing 1h10 first A.
If she has a good nap (1.5h or more), also add 10 mins to her second A time and hold for 3 days.
Same with the third A time, add 10 mins and hold for 3 days.
Skip the 4th nap/CN and aim for a 12h day.
After 3 days, add another 10 mins to each A time. She is well behind the averages for her age so you should be able to push fairly quickly even if she is high sleep needs. At 5.5months a minimum would really be 2h15-30 for most babies, some are easily doing 3h. But if you jump there all at once she will get very OT. Slowly does it, extend your A time, work towards two long naps and shortening your third nap to a CN.
And then read this:
All about the 3-2 transition- 5/6 months to get from those 3 naps to 2!
Good luck, let me know if you have more questions