as long as her kid isn't half your age minus 3 or older then you are set
example: you are 20, the kid cannot be older than 7 or you are fucked.
I used the rule in gym class back in high school two years ago, with pushups, teacher says do 10, i say fuck that divide by 2 minus three, i did 2. its a good rule to live by with anything that might be too much.