We have a border collie - 2 years old female.
Problem with her behaviour now 2 months past her rutting season.
She snaps at our guests and is seems nervous and uneasy.
Also she behaves likes she is going to have a puppy - she treats one of her toys as her puppy.
Until now she has not been like this.
Being a border collie she is very protective by nature, but also we find her very cuddly and somewhat jealous.

Previously she had a thuja for some eye infection (which came after her vaccination one year ago). Also she had a phosporus for a yellow diarhorrea which lasted many days. Thats more than 6 months ago.

Any remedies spring to mind? Is sterilisation a good idea?

I would get her spayed. You could try using bergamot spray.