Need advice for semi feral cat

Recently my husband and I found an outdoor cat we had been feeding was pregnant. She had 5 kittens,so we took them all in (in addition to 2 cats we already have). By 10 weeks we were fortunate enough through a rescue to get all babies homed. We decided to keep momma cat. We had to have a mobile vet come check her out bc she was too skittish to get into a carrier. The last kitten went home a month ago. She has been living in our only bathroom which is quite challenging but there is no other room in our tiny house to use. We have recently been letting her out to explore but one of our cats is territorial and hisses at her. Last night our feral began to cry a lot. It's very high pitched. She still needs to go to a vet office to be spayed. I thought maybe she was in heat but she isn't acting like our other cats did in heat before they were spayed. I am not sure if the other cat has stressed her out or what. I want her to be happy here and not sure what sparked the sudden crying. It's 5am and I've been up with her most of the night. Any ideas?

She very well could be starting her heat cycle.  You are best to get her to the vet to spayed ASAP.  It will be easier to socialize her and introduce her to your other cats once her hormones are shut down. 

Here are some guidelines for introducing cats.  It can be quite a process and the key is to take it slow and steady.  Have you done any scent or site swapping yet?  Site swapping may not work if you cannot pick up the new kitty as you will need to get her back into the bathroom.  Yet start with scent swapping.  Below are the articles and a video.

http://www.thecatsite.com/a/the-ultimate-yet-simplified-guide-to-introducing-cats

http://www.catbehaviorassociates.com/a-simple-little-trick-to-use-during-new-cat-introductions/

http://www.aspca.org/pet-care/virtual-pet-behaviorist/cat-behavior/introducing-your-cat-new-cat

http://jacksongalaxy.com/2010/10/01/cat-to-cat-introductions/

Think you are right as her yowls drew the attention of another cat to meow back at our window. Yikes. I'm going to try to get a vet appointment asap. I have not tried the scent swapping but that sounds like a good idea. Thanks so much!

I agree on that yowling,  it sounds like she's in heat,  my friend up north has a un-spayed female in the house and she says the same things you do,  and I do agree that maybe her outside time may be less stressful if she's not in heat and getting along with the main male outside may take some time and a little supervision,  either way,  best of luck............

Agreed on all of the above - I'd be stunned if she wasn't in heat. While cats generally act similarly when in heat - some make a lot more noise, or become more friendly, than others. Definitely a vet visit sooner than later! She'll be easier to deal with in so many ways if she's spayed. And healthier for her too! (and healthier for your nerves and those of any cats within a big radius!).