My 90 year old aunt passed away and we have a copy of her latest will but no a signed copy. Is this valid?

There is a provision in the Probate Act that allows a copy of a Will to be probated when the original is "lost". Unfortunately, you do not even have a signed copy of the Will. The attorney, apparently, can confirm that your aunt signed the Will and took it with her; however, that does not necessarily mean that she intended that Will to be probated. Maybe she changed her mind and destroyed the original. If there is no Will that can be proven, the of intestate succession dictate who are the beneficiaries of the estate. In other words, her heirs will get her estate. Her heirs would be a surviving spouse or children If there is no surviving spouse or children, but there are surviving grandchildren, they would be the heirs (not great grandchildren). Someone will need to open the probate estate. Anyone could attempt to introduce the unsigned Will, but I doubt the attempt would be successful. If everyone gets attorneys and fights over everything, her estate could be frittered away with attorneys fees. Hopefully, that does not happen. Reasonable minds should prevail. If you have the willingness to do it, perhaps, you should see an attorney and open the probate estate.