3.5 gallon pot

I’m growing a full crop as we speak however, I’m running low on my stash from last year and need something to smoke on. So I’m planning on bringing one of the girls into flowering stage about a month early than I usually would. I currently have her in a 3.5 gallon pot (the rest are in 5 gallon or larger). My question is that since I’m flowering her a little early, will the 3.5 gallon pot be sufficient to bring her to harvest or should I transplant her into a 5?

You'll be fine.
It will just require more frequent feedings/watering's

i use 3.5 gallon pots, but i use them as hempy pots with coco and perlite.
as long as the roots still have a little room to stretch, it should be fine