I'd get a very long leash or tie the existing leash to a long rope to she feels like she has freedom (you could then gradually shorten it over weeks if you feel the need to).
I'd also
create the situation for her success. Plan on spending a few days outside,
all day long. Take her water, food & bowls out there and take drinks, snacks, books, etc for yourself. I would keep her out there all day. I walk her around, have her drink. Walk some more, drink. Feed her outside, walk/play. Drink, walk, drink. She will have to pee outside!!! And when she does, praise her & tell her how wonderful she is & give her a treat. A couple of days of that & she should catch on
