I do, actually. Or else I wouldnt be asking this question.
You don't, because if you did, you wouldn't have your dog peeing on her property.
Unless you live in a very odd place, there are almost certainly public areas you could bring your dog to than someone's lawn. And presuming that by "her lawn" you mean her literal yard area, and not a nebulous area in front of her property directly adjacent to the road which tends to be viewed as a legal grey area for ownership (ie, the homeowner is required to maintain it, but it wouldn't be considered trespassing for someone to be there).
(And that's not even getting into assumptions about why you don't have a yard of your own or a public area in an apartment complex where you could do the same thing.)
Also, dismissing her being upset about it because you don't see why it should be an issue means you're not really trying to see things from her perspective. For all you know, she's wound up because she's had to deal with shit (literally or figuratively) from other pet owners who've caused her problems in the past, and you're just catching flack because of other assholes. Or maybe she's spent a ton of money on maintaining her lawn and she's afraid your dog piss will kill her grass. Or maybe she's bothered by the fact that you're literally a stranger wandering into her yard. Or maybe she's pathologically afraid of dogs.
Or maybe it doesn't really matter, because you're still the one going into someone else's yard, and they clearly don't want you there, regardless of whether or not you think it should be totally acceptable.
It's can be hard to stop a dog from peeing. Also, I know when I'm walking my dog, he'll run to the yard to pee on someone's grass. Most people in my area have pets and understand how they work. So, they don't really care much. Just because your dog pees in your yard doesn't mean (s)/he won't try to pee on other things. Also, he was going on a walk, it seems. He probably didn't just wander into her yard. He may have been walking on the sidewalk, then Reptar decided to wander in and pee. ---
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