Seniors age 65 years or older are less likely to sense and respond to changes in temperature. Your mom might not realize how hot it is and should be checked on often in hot weather. This is a big concern with seniors. Can she use air-conditioning or have friends/family check on her?
Does she have a Medical Alert system where she can push the button if she falls? If not, here is information on them: http://firstaid.about.com/od/Seniors/a/Compare-Medical-Alert-Systems.htm
One of the most common problems is dehydration, where elders do not drink enough water – this can cause her to feel or dizzy and fall. Tell her to drink more water throughout the day when it is hot, and check on her often.