“Tho” is a shortened form of “though.” You are more likely to see it in text messages or in very casual writing by young people. “Though” is used to emphasize a contrast, such as in your sentence above: the contrast is she was sick but she seems better.

Putting the “tho” (spelled correctly as “though” which is an alternate form of “although”) at the end is informal usage. It’s better placed before “she seems better today.” Then you can probably see it means “but”, more or less.

though