all you do is control how fast she walks with the lead, if she starts moving in front of you pull her back. I know this for a fact that you can change their stride bc how do u think they do it in dressage, it's the same thing only on the ground. But i've had this same problem my 16.2h DWB had a super long stride and would do the same thing but that didnt compare to my 18h Hanovarian Gelding, by the way i'm 5'2 so yea, just control her more with the lead, when ur walking hold the lead about 6 in behind ur back so that will show her she needs to stay in line with u and not get a head. or if that doesnt work try walking with a crop in front of her chest held out horizontally and if she walks into it just push it into her chest a little bit.
"The horse you get off is not the same as the horse you got on; it is your job as a rider to ensure that as often as possible the change is for the better."