Not Listening To My Whoa!

Question
Ok, I got my first horse Charlie. She is 8 y/o, Quarter Horse, She is very responsive, not hot headed, has low temperament, she listens very well,and has had months of professional training for work with cows and was amazing at stoping with a simple "whoa"! So I take her home( I have rode her tons and got lessons on her before buying her) and let her settle in her surroundings for about a week. At the place she was at before she was inside all the time and had a indoor arena so she never really was out side. At my place I don't have an indoor arena and she has access to outside all the time. So I go to ride her yesterday and we are walking around and I say whoa, she listens, so I decide to get her into a trot, I say whoa, she slows but does not stop. So I pull lightly on her mouth, she stops. So I try again and again doing the same thing, she still does the same thing! So I ask her to lope, since she is outside and not used to be rode outside she goes a bit faster and I want her to stop, I say "whoa", she doesn't listen, so I pull a little on her mouth, she slows but doesn't stop, so i pull tighter and yell WHOA! Then she stops!!! I am so used to her stoping rich when I say whoa! I made sure that I didn't have any leg on or anything like that!
I am not sure what to do?
If you could help that would be great!

Thanks,
    Rianna

Answer
Rianna,

She's in an  unfamiliar setting, outside, with lots more distractions than she's used to dealing with.  Give her some time and reinforce her training with "whoa".  She just needs to be reminded that the same rules apply.  Work first at the walk, over and over then advance to the trot.  Same thing.  Make sure she's responding correctly before you move on to the lope.  She will pick up that things haven't changed even though the setting has.