And does this early BT treated as nap issue come up every time a nap is dropped?
I don't remember mine ever doing this so I think it depends on the LO. We did sometimes have OT waking in the first part of the night when he dropped a nap, waking at say 20 mins but he certainly didn't think it was a CN he was just very very tired and OT.
Here's a different thought - how about increasing the A time between nap 1 and nap 2? That A time is very short for 5 months and now that you are getting a good first nap she can likely handle longer A, it could also encourage her to nap longer for nap 2. I'd probably increase to 2.5hrs (first to 2hr 15 then after a few days 2hr 30). If she didn't nap longer then it just helps to move the day on so that you get a slightly easier routine running up to BT.
S 1.30 - 2.10 (if it stays short)
A 2
S 4.10 - 4.50 (if it is still a CN)
A 2
BT 6.50/7pm
The EBT is avoided and so is the late 8pm BT.
if second nap extends then something like:
S 1.30 - 3pm
A 2
S 5 - 5.30 (CN)
A 2
BT 7.30 slightly later BT for a few weeks, around 6 months she might be able to go to 3hr A which moves the naps later and drop the CN.
I know it's not exactly what you asked but hope this might help.