What is a healthy heart rate for a teenage girl?

For about 1hour i've been feeling weak and getting weird sensations in my chest - such as it feels cold and "ticklish" (no other word to describe it, sorry!). I checked my heart rate 5 minutes ago because i have a history (more than 1 year ago) of fainting unexpectedly and it was 52bpm - would this be considered too low for a teenage girl? I heard from my mum that teenagers have slightly faster heart rates that adults however I can't find any info specifically about teen heart rate.