Dear Sam ~ Your friend needs to bring his girlfriend to the hospital for an immediate evaluation. He needs to take her threats VERY seriously. She is not stable and until she is on the proper meds and is acting this way she is a threat to herself and others. If she will not willingly go he MUST call the authorities and tell them of what happened and insist they take her to be evaluated since he is afraid of her harming herself, him and/or their son.
I don't know how it is in England but here in the states anybody who threatens to hurt themselves or others will be admitted for psychiatirc evaluation and treatment.
PLEASE talk your friend into getting her help. If she refuses he must call the authorities. She needs help ASAP to prevent her from harming herself or others.
Please keep us posted as to what happens. You are a great friend to seek advice for you friend ~ Goody