Isn't that Ashley's armor?
Ashley's armor is pretty much the heavy Phoenix armor, though it's medium when we first encounter her on Eden Prime, likely because her level is lower and heavy armor has yet to be unlocked for her, same as Soldier Shepard. The armor in the OP is similar to the light Onyx armor that FemShep and Liara can wear in ME1, though the bits on the shoulder are specific to ME3's design.
If you mean this one, it was my favorite of hers as well:

It needed a helmet though.
This is my favorite armor for her, so it's the only one I use. I do like the black one, but the only time I ever have Liara wear it is during the Citadel DLC and nowhere else.
As for the helmet, I wish it had one too, though Liara's choice of "helmet" was pretty much ruined since ME2 in LotSB, which is weird, because ME2's prologue had her wearing a full helmet just fine.