well without knowing any other information about your mother's overall health i can say that sounds like a wonderful blood pressure level for an 87-year-old. usually blood pressure increases as we age due to some natural stiffening of the arteries. i'm not sure if you're concerned this reading may be too high or too low. a blood pressure reading of 120/65 is pretty normal. the second number 65 is a bit on the low side but that's not a number we're often concerned about. the first number is the more significant one. it should be below 140 and above about 90. if your mother is experiencing symptoms like dizziness feeling faint nausea or anything new and unexplained then you might want to seek medical attention. but just based on the blood pressure numbers you gave (and not knowing anything else about your mother's medical history) i don't see anything worrisome. wishing you well!
my mom is 87 her blood pressure is 120 over 65 i that ok