Lola getting bully when I walk her outside

Recently, I feel very reluctant to walk Lola outside. She doesn't pay much attention to me after walking out from the gate of our house, but only sniffing, and use up her bully energy trying to pull me here and there. I guess she completely forget about the "heel" command. Besides, sometimes she acts like sleeping beauty, lying down gracefully when I command her to follow me while she reluctant to do so. What can I do? I can't lift her, she is over 40kg now... She is really become naughty recently. However, of course, when back inside the house, she is still my sweet baby, good obedient girl. I really need to put her back in "heel" training again, hopefully can make it.