For the mother of a newborn to write the following is a sign of someone who is mentally unstable and who is plausibly a danger to herself or others.
[I find no joy, no pleasure and no love being a mother. I can't sleep knowing I must wake up to a crying baby and the same routine of feeding, diapers, baths and bottles. I have become more and more detached from the girl and have nothing to enjoy. I can't even enjoy a cup of coffee without looking over my shoulder to see where the girl is. I don't want her to touch me, and I can barely hide my revulsion. I am exhausted beyond belief, and my thoughts are turning darker every day. It's not the girl's fault she was born, but I can't help feeling resentment and anger toward this little person who more and more resembles a block of concrete on my feet.]
She needs medical help and her child needs to be in someone else's care, immediately.
I believe this letter to be a hoax but if not, then when she brings the baby for a checkup she could easily tell the doc about her feelings and get a referral.