Hey hun, I hope you feel a little more relaxed now you know you have some more time off.
Your work are acting in completely the wrong way and you should definitely put a letter of grievance in writing to either HR or her line manager. They should have a full grievance policy in place which they have to follow by law.
It may sound strange but start writing a diary logging dates and times and quotes of what has been said and sent to you. If the grievance gets taken further then you have some evidence of what has happened.
It is totally wrong of her to tell other members of staff why you were off sick in the first place, this is a breach of confidentiality. And to top that her first comment to you when you come back is just disgusting.
Like the other girls I am actually raging about this, I can't believe there are still managers out there that think this is acceptable. If this carries on I think the girls on PF will be round there mob handed to tell her ourselves!
Stay strong honey, stay strong, don't let the bitch get you down!