As long as the number they expect shows up at the time they expect and with a name or confirmation number that they expect, then the folks at check-in don't really care who the people are.
I always book all ADRs with my name when planning a trip, even if I do not intend to be present at one or more of the meals - especially when travelling with a larger group, everybody isn't going to be at every meal together.
If you give your mom's name/confirmation number and have the party size listed on the reservation, you will have no problems. They do not ID the person checking in.