Well you didn't really provide much information, but I'll try to help with the info you did give.
If you are your mother's only child and she doesn't have a spouse, that makes you her sole heir/beneficiary to the trust.
If you die before she does, or a little bit after...your share would then go to the next person specified in the trust agreement...unless your wife is listed as the beneficiary after you in the trust, then no, she won't automatically get whatever you would inherit. Do you have children?...if you are an only child then most likely your share would be divided evenly among your children.
YOU need to draw up a will yourself and your wife as your sole beneficiary if that is your wish. Some trusts specifically require an heir to survive the deceased by a certain amount of time in order for the heir to receive the inheritance. If you were to die before that time period, then the trust would be divided among the next heir listed in the trust after you OR your children if no other heirs are specified.
If you do not have any children and you die before the time of survivorship specified, it will get very messy.
I recommend you tell your mother to list your wife as the beneficiary after you in her trust agreement to make sure everything goes smoothly.