Just saying you're "going on a trail ride" is kind of vague. You really need to know your horse, and know what kind of work she has been doing over the winter and early spring months, and have a general idea what kind of shape she is in just riding her in a more controlled place (like an arena, or pasture).
If she's huffing and puffing, breaking a sweat and getting winded after short bursts of running and playing out at pasture, you're going to want to tone down your trail ride and make sure you pay attention to her behavior along the way to be sure she doesn't over-exert herself. You can do a longer ride, maybe, if you take it slow and give her breaks when she's getting tired.
Some horses (like mine) will keep on going, no matter how long and far they've already gone. I've known some that will get themselves sick because they just won't stop. They don't know when to quit, so it's really important to make that choice for them.
Just remember, it's supposed to be fun. Take some shorter, easier rides if there is any doubt about how fit she is. Work your way up from there.
"Parelli horsemanship is just like painting by the numbers. You need absolutely no skill. You just put this color here and this color there, and when you're done, you have ... a mess no one wants." mp