How do you tell the context in this sentence considering mañana can mean both yesterday and the morning?
«Mañana» means "tomorrow", not "yesterday", and it's easy:
- It doesn't make sense to translate «mañana» as "tomorrow" if there is a "this" before it.
- The word «Mañana» is masculine when it means "tomorrow", and feminine when it means "morning".
Your saying it dosn't mean "yesterday" yet when you click on the word for a translation it literally says "yesterday" and "tomorrow."
The "hints" are not necessarily correct. They may even deliberately include wrong words to see if you make common mistakes, for example offering both «la» and «el» for "the".
Duo then learns that you need practice on that word and will slip it in during later exercises.
Learning though making mistakes is a very effective teaching method. If you are not sure, you can (and should) always check in a dictionary. There are lots of online ones like SpanishDict, Linguee etc.
I wrote we aren't running this morning to see if duo would accept non past. It didn't.
It depends on who is making the statement. If it's a group of women, then you use nosotras.
If you listed carefully you'll hear "nosotras" not "nosotros." Okay. But it's a guy saying it.