Yes, it is true, It could still be just a molt...Let's hope so as It is the season for molting, and I really considered that...BUT...
When I have a bird with lingering loss of feathers only at what in the photo appears to be around or below the vent, with redness, and if the bird has sustained significant stresses, I definitely check for pests or illness. I definitely would with this bird since isn't this the bird that was kept in very unclean and harsh conditions? And, after 2 months, it appears only this patch is what is effected, the molt after 2 months has not appeared (in the photo) to advance to other areas...I would then suspect pest/illness rather than simple molting.
My birds typically molt around the tail feathers first and/or the base of the tail on the top, working its way up and around if a harder molt....but each bird can be somewhat unique in their molt pattern, and some birds molt harder and take longer than others leaving patches for an extended time. Here's a sight that shows "typical" molt patterns and one with the possible causes of feather loss and solutions:
http://timbercreekfarmer.com/animal-care/help-my-chickens-are-molting/
http://www.the-chicken-chick.com/2013/03/chicken-feather-loss-cannibalism-causes.html
When you look closely at the patch, if it is a molt, you should be seeing pin feathers starting to regrow. You should see no other signs of creepy crawlies (dark specks which are dried blood trails from mites, or yellow creepy crawlies skittering away as you fluff the feathers above and below the vent....look at the others links I've provided for those too. You should not smell a cheesy or really off odor (taking in consideration it is a chicken's bum...but it should not smell strong...I don't notice a smell from my chickens at all when I examine their vent... only when they actually just pooed, and then from the poo itself.)
If, let's hope, it is just lingering molt in this bird, you can support her system better to help with regrowth, especially if she is the one that was in the rescue situation. Giving extra protein and Black Oil Sunflower Seeds (BOSS) can help provide the extra nutrition. I also like the Rooster Booster Multi Vitamin, or better the Multi Wormer as you then worm and boost nutrition during harder times of stress.
This season I've used Nutrena's Feather Fixer to help my birds recover from a terrible lingering molt (began in early August!) I am skeptical with any commercial product with advertising, but the Nutrena Feather Fixer was getting good feedback from the community I live in, and it DOES seem to help birds regrow feathers during the molt. I have to say they appear to have recovered much faster this year as all of them are really coming into full and glossy feathers about 2 weeks after being on the feed. Nutrena's Feather Fixer also has some ingredient (not a chemical, not a drug according to the company) that is supposed to help discourage mites by creating a poo that is less pleasant for the mites....Nutrena is pretty tight lipped about what the ingredient is (I can't find it on any google search or company literature), but I suspicion it is some herb such as garlic or such that simply leaves an oily residue at the vent site...for me it was worth a try for feather regrowth and boost nutrition right in the feed...it also contains probiotics.
Good luck figuring out whether this is a lingering molt with a rescue bird who needs more support to get over it, or if there are darker forces at work. Even if it is lice or mites, or a mild case of vent gleet, with proper treatment the bird should recover fully and soon have a nice fluffy bum again....even though it may take a little time.
Lady of McCamley