Also daughter will no doubt want to ask her mom what it is like. I am wondering if I should quickly steer the conversation into something else
no, don't steer it to something else. Your daughter is 14 years old, she is growing up whether you want it not. She isn't as naive or innocent as you seem to think she is, unless you've kept her in a plastic bubble away from all else her entire life. Seriously, visitation at a prison isn't as bad as all that.
Just take her to see Mom and just let them have their talks.