Co-sponsor documents: Originals or copies?

For my spousal visa application, my mother-in-law is acting as our financial co-sponsor and as a provider of temporary accomodation until my husband and I find a flat in the UK. I have an original letter of intent and support from her, a copy of a mortgage statement from her building society, a copy of a recent council tax bill and utility bill, copies of her pay stubs for the last three months, copy of her passport and an original letter from her employer.

Are copies okay or do we need originals for her documents? I don't think she feels comfortable sending originals in the mail. We'll have originals of our savings info, original marriage cert, original passports, birth certs, etc.

Thanks for the help. 

We had notarized copies of deeds of the house that my husband partially owns and had no problems.  They were notarized by a lawyer in the UK.

What if they're not notarized, just copies?

If at all possible, have originals.  If you can't get originals, take notarised copies.  When DH went to apply for my visa, a couple of people were turned away because they had non-notarised copies.