Looking for answers

My mother in law is up for a visit for a week. She is 72 yrs old type 2 diabetes and she takes Lantus. My question is she says she only needs to take it if her sugar is off...is this true? I thought no matter what your sugar reads you always need to take the amt. prescribed each day. I asked her tonight when she tested it if it was good she said yes...so she said she didn't need to take a shot..I asked her well what if it's good tomorrow morning? She said the same thing that she wouldn't need to take her shot..again I think this sounds wrong, could someone please help me to understand this? Thank you.