The 2 witnesses to Mary Ann's marriage on 25/12/1875 were Jacob Humphreys and, as already mentioned, Esther Brookes. This couple married each other just 1 week later on 1/1/1876 and Esther shows her father as James Brookes, deceased.
I feel absolutely sure that these 2 were sisters - however, I'm having just as many problems finding births/baptisms and on census as before.
Possibly found Esther in 1871 living in another household as a lodger in Manchester.
One thing I keep coming back to is this:
1861 Census - Chorlton upon Medlock
Mary Brooks Widow. 32 Framing Tenter Cotton Mill b. Stockport, Cheshire
Esther Brooks 9 (incorrectly transcribed as Catherine on FindMyPast) ditto
Mary A. Brooks 7 ditto
Yes, all 3 are shown as born Stockport but if the 2 girls were just infants when they moved to Chorlton when they grew up they may not have realised they'd been born in Stockport.
I also found a baptism on 15/4/1855 Manchester for an Esther Brooks, dau. of James and Mary. It's just a transcript on FindMyPast and no idea which church it was, nor the occupation of James. Was hoping to find Mary Ann baptised at the same time (late baptism for both) but no joy.
Forgot to note exact details but found a Mary married to a James in Stockport in 1851 - no children yet, think it may have been under Brook on Ancestry. Sure she was a Tenter.
Maybe some red herrings here but my gut instinct is that Mary Ann and Esther - both with a father James per their marriages - are sisters and the 1861 census above is the only one I can find with possibly the 2 girls together.
Will leave this to you to ponder.
Annette