Girl I liked on Facebook suddenly says hi!?

[Anthony Nguyen]

This girl(Isabella) suddenly says hi out of the blue out of all our years after my friend asked if she liked me or not.What does this mean?What should I say?(we have dated before)all she says is ya while I always make up things to say.By the way when we dated(2 times)all we ever dead really was wave at each other in the hall smile at each other when we see each other and talked only alittle.
I've already chatted with her this happened 3 days ago.

[Black Jack]

say hi back??