Hi there and welcome:)
I doubt she is ready for 3 hours A time at 4 months - that's a bit much and she would accumulate OT in the process. It's possible that 2 hours is less but add just 10 minutes and see if it makes a difference. Hold at this point before you add any more. There is a sleep regression + long and difficult wonder week at 4 months, so this could simply be a phase (and I think it is) Tired signs do tend to get unreliable as they get older, and it is good to keep an eye on the clock as well.
However, 2 x 2-3 hour naps + a CN does seem like an awful lot of sleep. Could you post what your day looks like. It's possible that you don't even need that CN if her naps are so long. Basically, you need the pm nap ending at a point which doesn't leave too long a gap to bed. You want her nice and relaxed at BT, not awake & jumpy or over tired. If the pm nap ends too early, maybe you could do a short CN - 10-15 minutes only and then proceed with BT routine. If a long CN is pushing your day so late, it is best to tweak it.
We also moved to a routine similar to yours at 4 months. We would get a long first nap and then 2 x 40 minute CNs. I would move straight to BT routine after the evening CN, which was ending at 6 most days. BT was 7pm always. My DD always did her shortest A to bed.
You could definitely incorporate a dreamfeed. We did it till 8 months and it was great!