Working theory: Lissa is closer to Uncle John than Mate is.
Lissa does not live in Montour Falls. Lisa does not live in Michigan.
She is also mentioned, as "Liss", in the April 28, 1889 letter.
Working theory: Mate "up to" Uncle Levis. Mate spent some time living in Ovid, NY. That is north of Havana, using the "up=north" idea.
Was the fact that Helen came home the inspiration for the visit?
Helen has a connection to Mansfield, PA but is "not going back".