My daughter is 14 years old at this time, but at the age of 13 she had a sexual encounter with a high school boy aged 15 or 16, I am unsure at this time. She advised me that she didn't "really" want to do it, but didn't know how to say no. Is there any legal action that can be taken against the boy in this situation?

If the boy is more than three years older than your daughter, he would have committed sexual battery, and prosecution can commence up to 10 years past your daughter's 18th birthday. If he isn't more than three years older, there's not much action you can take. Legally speaking, your daugther was capable of understanding the nature of the act, didn't resist, and wasn't prevented from resisting due to mental incapacity or force, so no laws were broken by the boy.