Hi!
If her rear end was dirty with poo it could mean watery poops (no solids passing) and the brown liquid coming from her mouth would indicate to me that she has an impacted crop that has gone sour. This condition is called "sour crop". You can confirm this (or rule it out) by holding her and feeling her crop area (preferably in the morning when it should be empty). It will feel like a squishy water balloon and this is not good. If her crop is not like this...it is something else. To further ID this condition, you should smell the brown liquid. It will smell foul and...sour. The bird's breath will smell bad too. If she has none of these symptoms, you can disregard the next paragraph.
Ok, assuming this is sour crop, there may be other ways and I'm sure all kinds of experience and information will be shared here.
The way I handle this is to first get the bird to vomit, cleaning the toxic and rotting contents of her crop. You tube videos are great for providing visual references and additional info. It seems daunting at first but you get used to it and remember...it's for her benefit.
Following this, you need to isolate her with nothing but water for at least 24 hours. If she seems too far gone to drink on her own, you will need to give her drops of water. You can also use a poultry vitamin-electrolyte mix if you have on hand. No food at all...she can't pass it so it will only contribute to the problem.
While she is in isolation. Message her crop several times daily to get things moving and hopefully you can move the blockage.
After 24 hours, I give the bird olive oil soaked bread...I mean drenched! The oil coats the crop and it's contents and can provide lubrication for passing the blockage. Don't over feed..this bread is more to get the oil down in her crop. Keep messaging throughout the day.
Following this you'll need to monitor her for a few mornings before releasing her back into the flock. You need to make sure the blockage is gone before she goes back to eating as she normally would or it will be all for nothing. During this period give her easy to pass foods. Soft foods. I like olive oil soaked scrambled eggs, mashed bananas and a little soaked bread.
I've never tried it before but I think some people use monistat 7 to kill the problematic yeast in the crop. Someone here may be able to provide details but I'm sure there's something online if not.
I wish you the best of luck!