My Mom sold her house and now resides in our home. What taxes should I be aware of in this transition? She is 81.

[Bsch4477]

If she owned and lived in her home 2 of the last 5 years she can exclude $250,000 from her capital gain on the home sale. Her gain is the net selling income minus any capital improvement costs. If her income is low enough she might also escape more of her capital gains tax. 

[Hal_Al]

If the home had been previously owned jointly by both your parents, half the cost basis "stepped up" on the death of her husband (the entire cost basis stepped up if they lived in a community property state).  This would reduce the capital gain amount.