I have different questions so 1- i have a dryer bu...

Your humidity is in a great range and shouldn’t develop mold. So long as you combine it with proper air circulation you shouldn’t experience any issues at all. Also it’s fine if your plant is slightly behind. It may just not be getting enough light if it is tightly cramped next to the other ones. Good luck on your grow!

If your dryer can't get below 54%, you have a perfect drying as you do not want to dry your harvest at less then 55% or you'll lose terps. Also, temps need to be =<20c or the same (terp loss). I dry mine to 70% humidity, the put them in brown paper bags to 65% humidity, then into glass jars (burping once a day) with a 62% Boveda humidity pack to get it down to the perfect (for me) 62% curing humidity.

1. No is not a problem. My humidity is normally around 65% and to protect my harvest I raise the temperatures of the drier to over 20°C (68°F), try to keep warmer temperatures and it will protect your buds. I use a cardboard drier and put it inside the growbox with the lights on, so to raise the temperatures; also I put silica sachets inside the drier (like the one that comes in shoe boxes).
2. Yes it's normal, even for same strains, to develop at different rates, don't worry.

Hi there! 1/ Not if your airflow is good but 30% would be better, in order to avoid rotten buds. 2/ She might be suffering or recovering from a previous mistake. I see your pH is 7, that's not the ideal level, your pH should be in a 6.0-6.5 range. Otherwise this can come from genetics, even if they're all the same strain, you can have different phenotypes. I won't worry too much at this stage but keep a close eye onto her growth. I'll be around, keep us up-to-date and happy growing!