I'm certain that's the case. Remember last week, when Shane had his partner (Army) hold back a couple of bags of coke (or smack or whatever the hell it was) from an evidence bag after a bust? I'm sure Shane's sneaking them to Mara.

Im not so sure that she's using as Im convinced since last year that her mental state is hanging by a string.

did they show what she was pulling out of the cabinet?
when she bent down and reached in it when vic left I figured she was grabbing some drugs to shoot up

If she's using, I hope they are using formula for the baby!