A rosary is not a magickal item unless it has been blessed or concecrated. It isn't naturally powerful like sea water, salt, herbs, stones or any other natural items. So because of this, if you hold in your hand a plastic rosary then you're not holding much. The best rosaries are made from natural ingredients.
Plastic doesn't hold energy very well. Now, I happen to own several rosaries, as a matter of fact there's a large crucifix right next to me. I got this when I took a trip to Mexico and it was actually for my grandmother. I felt it would "complete" her altar but she has passed and I have kept it as a memory of her and as a symbol of my faith of course. I go to shops and if I see a rosary section I just have to stop and check them out to see if there isn't one I'd like.
Anyone, no matter their religion, or lack thereof, can touch a rosary. Someoneone Satanic could be sucking on a rosary and NOTHING will happen (unless of course they swallow it and choke haha but that's a different setting). Even if it is blessed nothing will happen. You can serve holy water to witches and satanists and nothing will happen other than receiving a few blessings from you.
So if the rosary was a gift from someone, whether they claim to be witches or not, they could lay a sort of curse on it without even knowing. Everyone has the same abilities to bless or curse no matter your faith. If someone gives you something and bad stuff happens then chances are they don't really like you or were upset with you and unintentionally served you a curse through the gift.
If a witch gives you a rosary for protection, that is like receiving it from a priest. These are people who know and understand the power behind certain items and how they can help you.
Crosses are said to be protective because they create light from their center. So yes they are protective but only when blessed especially if they are made from unnatural items such as plastic. Wood crosses are good. If your rosary is giving you grief then cleanse it. The easiest thing I can tell you to do is to go to church, submerge it completely in the holy water and attend mass as usual. After mass ask the priest to bless it for you. You're done! Problem solved and you can begin to enjoy a more protected self.
Blessings,
Shadow Storm
A Chrisitan Witch