Urgent question regarding Obamacare

I apologize for posting a new thread regarding this matter.
I am sure this topic has been covered in this forum previously.

My sister is currently working for a company, and the company offered her to assist half of insurance cost. She still will have to pay close to 300 a month. I understand we will not be fined since our status is under DACA.
She was going to tell her employer that she did not want the insurance but her HR manager told her that she will be fined and it is mandatory to have health coverage.

Do you guys recommend taking this offer?
If she decides not to take the offer will she be fined? will company be effected?
Will she be able to cancel her coverage down the road, lets say in few months?

I understand I should have obtained more information regarding Obamacare before this shitstorm, but I guess its already too late.

Any advice for my sister is greatly appreciated.
Thanks so much.

by the way shes full time working under W-2